You might be looking at this from the wrong angle
You see, it's true that chompers are egg shaped creatures and really seem like a tougher and less friendly version of humpty dumpy who lost a pair of limbs, but the truth here is that their similarities basically stop at the shape.
Let's look at one of the predators you mentioned: egg eating snakes have a great sense of smell, which is very important to them. Why? Not only because they need to find eggs, but because they need to know which of said eggs have been recently laid, because these snakes simply swallow an egg, crack it with a protrusion of their spine, squeeze the liquid out into the stomach and then vomit the shell, problem is, they can't really digest an egg with an embryo already forming in it, so they're already outside of the question.
Your chompers may look like eggs, but a chomper predator won't really be something that eats eggs that put up a fight, they'll look more like the predators who regularly feed on armored prey. Arthropod eaters, armadillo predators and things that eat crocodilians are much better contestants in this situation.
With that out of the way, let's talk about why THE OCTOPUS is once again the best- I'm joking, they fit the criteria of predator that eats hard shelled prey (especially crabs) but this time there are better examples to base our predator on:
1-Jaguar: these are the definition of an overpowered animals by natural standards. They're fairly good at climbing, they swim well and they have the strongest bite proportional to size of any feline. What does that mean? That they can easily eat Turtles and crush the back of the skulls of caiman and other prey. Aka they pack a mean bite, and the fact that they have great climbing and swimming skills (plus a running speed of around 50km/h or 31 mph) means a magical variation of a jaguar could most likely deal with your chompers' annoying armor just fine.
2-crocodilians: when it comes to cracking something, pressure and strength are important, therefore it's not hard to picture that the group of animals that pack the strongest bite in the modern animal kingdom couldn't be left out. Much like jaguars, some crocodiles also eat Turtles. A little less like jaguars, crocodilians also have the habit of dragging prey they can't easily finish into the water and drown them, something that usually involves them performing their infamous death roll. With this set of skills, powerful muscles and great swimming ability, I don't doubt they could deal with a chomper.
3-spiders: while not as large as the other examples, spiders have a group of behaviors that make them be mentioned here.
One-many spider weave webs and other traps meant to, well, trap their favored prey, from nets, strings of silk with glue at the tip to even no webbing at all, they are a group of successful hunters that also hunt prey with shells as tough as theirs.
Two: some spiders are known to integrate iron into their fangs throughout their lives, so that they are tougher than the chitin armor they need to pierce. Some spiders at the end of their lives will have fangs essentially made of metal, which is precisely what would help penetrating a tough shell.
Three: spiders ALSO like to "spit acid", except that they don't spit it at their prey per say, they inject it. Spiders are known to preform something called extracorpoeal digestion, meaning that they'll inject venom into their prey, which will both paralyze it and liquefy its insides after some time, at which point they'll simply drink the solution, turning the annoying shell into a convenient bowl.
Now that we've clarified a few slightly better contestants, let's elaborate on one necessary rule: no matter what these predators are, they most certainly WILL HAVE or at least will need some level of chomper acid resistance or countermeasure. if chompers are their main prey and we haven't completely abandoned natural selection, chances are that the animals which didn't have any resistance to it died or weren't ass successful in breeding (due to severe injuries), with the other alternative being that the successful ones learned how to force them to puke it all out before safely finishing them.
With all of those done, the easiest option would be to just "magic-alize" these animals so that they can fit into your world (yeah you'd have magical giant spiders but we have magic, the square cube law has little power in here).
Another, more interesting option would be to make a magical hybrid that mixes their best traits. A good example would be a reptilian version of a jaguar with a skull slightly more remiscent to that of a crocodile, packing an even stronger bite (also add in a dunkleosteus' plates instead of teeth for both slicing and cracking potential, with traces of iron in them for additional toughness and more pressure at specific points) and being in between endothermic and exothermic, with a thick armor of osteoderms to help it resist the chonper's acid and powerful limbs for climbing, running and swimming (maybe even make the tail something in between crocodile and jaguar for some additional aquatic prowess and a strong tail swipe ability at the cost of some mobility [unless you also just magic it so that the tail doesn't hider it at all cause impossibly strong and dense muscles]). Another thing important to mention is that, most likely, it will be smarter than the chomper (potentially plopper level intelligence at least would be the ideal scenario), since their natural abilities won't be much useful if their prey can easily outsmart them and throw a bucket worth of acid into their mouths Godzilla 2014 style. I'm fairly certain this deathjaw (that's what I'll be calling this magical animal) would certainly be more than able to hunt and eat chompers just fine. Regarding acid resistance and countermeasures, they might simply rely on their scaly armor, or also pin the chomper down and fool it via patterns in its long tail to make it think it's a head and make it puke all of its nasty acid out, finishing it with a powerful bite and eating its soft insides peacefully. Regarding size, making them the size of a slightly bigger jaguar or even allowing it to get as big as a saltwater crocodile (around 5.2 meters or 17 ft long , with about half of it being the tail) will be up to you, just remember that if their Jaws must at least be able to fit a chomper inside them.
Now, while still focusing on the deathjaws, could they deal with the evolved chompers? Well... Let's first sum up WHAT they'd need to hunt.
Glutton: is as big as a small car, can vomit out enough acid to fill a tub, an acid that's 4 times tougher than a chomper's, are as heavy as an hippo and can somehow support their weight while climbing walls, aka very strong legs.
Savage: is as big as a bear, can and will ignore even life threatening wounds, are almost entirely covered in an armor that's essentially on the level of some metals, are armed with large razor sharp talons, are about as smart as a human being, are able to MAKE AND USE TOOLS and are presumably also equipped with great speed and sharp reflexes due to how well they can dodge.
So? Can a deathjaw hunt these down? Maybe, if we give them lazer vision and a super saiyan transformation, because I'm fairly certain that nothing that's ever walked on this lovely planet could get close to beating them, unless they were to stand completely still and let a sauropod squish them dead. One of them is a bear on steroids with the brain of a human and knifes for claws, the other is essentially a living tank that can shoot extremely potent magic acid out of its mouth. Even if we were to say dewthjaws hunt and live in large packs, they'd likely still wouldn't be able to even fight these things for territory without expecting massive casualties and a lost battle. The only way for them to be able to perform these feats would inquire at least 2 upgrades so that we don't make them just mutated humans on steroids:
1-their acid resistance is now at glutton level, meaning they don't really need to worry about what the chompers produce because they can handle much worse.
2-They have the magical ability [sizeshifter], which allows them to freely scale their size up and down according to the situation without the issues that'd arise from such variation, aka they can turn small without freezing and become large enough to make a glutton look like a chomper in proportion without getting crushed by their own weight, with their muscle power also scaling accordingly (meaning when smaller they can't bite as hard, but when bigger they can crush a truck under their Jaws). This way if they meet a glutton they can just grow and crush it as if it was a chomper, if they find a chomper they do as they normally would and if they meet a savage they just become smaller, climb on it and then expand in size, either pinning the savage down under its weight before crushing its head region with a single bite or simply growing until they crush it (and everything else around) and then just scrape their squashed bodies off the floor to eat.
Now that we dealt with predation, there's one last item to be checked: what about the calcification spell and it's effects on the deathjaw? Well this is relatively easy to solve, since the main problems of it seem to be located in the period between consuming the first chomper and eating the 12th one: while deathjaws are usually solitary in their young years, they are monogamous animals that mate for life and take very good care of their young. Deathjaws have a slow reproduction rate, raising only one cub at a time. When cubs are born, the males begin to hunt for both themselves, the female and the cub, while the female takes care of the child in a hidden den. The father will hunt for all 3 members while the mother will remain with the cub in their den while it "develops". Once the father brings a chomper, usually semi dead and with a half-cracked shell, the mother will finish it and feed their soft insides to the cub. While initially this will make the young one weaker and thus much more vulnerable (the reason why the female will never leave its side), once it eats the 12 chompers it needs, it will become significantly stronger, larger and more capable, at which point it will be considered as fully developed and will start hunting with both parents for an additional six months before it leaves its parents to live and hunt alone until it finds its own mate. This period is necessary for the parents to be able to properly teach the developed cub how to hunt effectively its 3 different types of prey and how to engage them. Thanks to this behavior, all deathjaws that make it to adulthood are essentially "skelly" variants of the species, since becoming a fully fledged skelly is directly associated with their development into young adults ready to learn how to hunt.
After all of this it's clear that I'm suggesting in the desthjaws a very overpowered creature that has an extremely powerful bite, sharp bony plates to both slice or crush their prey, a good domain over both land and water (they can swim well, climb well and run fast), a bony armor resistant magic acid and intelligence potentially on par with some hominids, as well as the ability to change its size at will to fit the situation it's in. The problem is that they need to be overpowered if they hope to fit the niche of predator to the evolutions of a chomper, which themselves are a mix of traits you'd normally only find in creatures that essentially have no natural predators as adults. So yeah, this, much like my plop predator, is something that will probably have no effort hunting down basically anything it finds. The only reason I think it wouldn't be a problem to humans is that chompers seek human settlements, which means that if you as a deathjaw ensure the humans are safe, they keep living where they are and thus keep acting as great Bait for your food. Also they've been sharing some food with you so no downs so far.
Edit: since I've already talked about both crocodiles and jaguars in a single animal (simply because I thought it'd be cooler to fuse them into a single more versatile predator that has the best of what they can offer) and you've asked me to introduce a version of our third contestant here it goes: how would a spider need to adapt to be an efficient predator for chompers and their evolved variants? Surprisingly, not all that much.
The slingers are a very special species of spider that doesn't seem all that special at first. Much like other ground spiders, they patrol on the ground hunting for prey. Unlike many other ground spiders however, they possess 2 very special traits:
1-while their bodies aren't all that special, their webs are particularly interesting due to them being both incredibly strong and almost completely unaffected when exposed to a glutton's acid due to being covered in a particular substance of unknown formula. While it doesn't mean that the web is completely immune to the acid, it does mean it can usually withstand it for a fair amount of time.
2-these spiders, for unknown reasons, also possess the [sizeshifter] ability, although unlike the deathjaw's version of this ability their maximum size is clearly defined and limited to that of a large black bear. This however doesn't hinder them much due to the way they hunt.
While they'll grow to larger sizes while looking for food in order to cover more ground, once they detect a chomper the slinger will immediately revert to the size of a normal ground spider, approaching it almost unnoticed due to its small size. Once it gets close enough however it will immediately increase its size and use its special spinnerets: much like other ground spiders, the slingers produce large amounts of durable and resistant silk that they'll directly shoot at prey at high speeds in order to immobilize them, and when it comes to the chompers, their primary targets are the mouth, gluing it shut, and the legs which will leave it stuck in place for more than Long enough for the spider to go towards its back and pierce the shell with its long, durable fangs rich in metal deposits. If all goes well, the spider then injects its venom, which spells the end of the chomper due to it being more than strong enough to paralyze its much larger and tougher evolutions. After a while, the venom will almost completely liquefy the chomper's innards, which will then be drunk by the spider.
When hunting gluttons and savages however, it's strategy changes slightly. When it finds a glutton it won't bother trying to keep shut a mouth that's mostly kept open, instead repositioning itself at the back of the glutton, shooting its web at the legs in order to keep it from turning fast enoug. It will then climb on its back to deliver the final blow. A desperate and starving slinger that failed to find other prey might even shoot web at its own legs if the glutton struggles too much, in order to prevent itself from falling from its back. This however can result in its death should the glutton free itself on time and roll over before the venom can kick in. In case of a savage however, the slinger will usually try to climb it unnoticed by either further shrinking itself to climb it or by climbing a tree and dropping on top of it. At this point, the spider will increase to its max size and immediately attempt to immobilize as many of the savage's limbs as it can, gluing them either to the savage's own body or to the ground. Once it's sufficiently restrained, the spider will use its Trump card, only possible due to their metallic fangs being mostly inorganic and essentially immune to the monster's acidic blood. Some tall tales speak of a slinger that tried speeding up a savage's death by repeatedly stabbing its neck and eyes. A slinger will only attempt to finish a savage if it manages to succeed at the initial ambush. If it fails, it will usually either sprint away or shrink in order to hide from it until it has a chance to escape unnoticed.
As to how it deals with the calcification spell: it usually "doesn't". As it functions mostly as an ambush predator that relies heavily on its special web slinging abilities to safely kill prey larger than itself, it usually doesn't need to worry too much about the period in which it's exoskeleton becomes more fragile, especially since during this period they're known for focusing mostly on hunting chompers and other less risky prey.