Depends on where magic comes from. As was once said, "Any sufficiently advanced science is indistinguishable from magic." and there is the inverse, "Any sufficiently understood magic is indistinguishable from science."
By it's definition, magic is 'not clearly understood power.' Up through the 90's before CERN was active and we detected gravity waves, gravity was technically still "magic."
So, running with that, here's one idea...
A "return of magic" means that something we previously did not understand or misunderstood that allows for it returns. For example, say there is a nanomachine remnent from a planet that exploded geologic ages ago, and our planet on rare occasion passes through this cloud of these nanobots that confer powers granted by this lost advanced civilization to sapients that happen to absorb some (or maybe it's not limited to sapients... fishermen may begin to fear groups of fire fish and hunters fear the mystic ice-ape or a afflicted Queen ant creates offspring of death drones). Maybe it was another planet in our solar system originally and a war on their world was so violent that it destroyed the planet, creating the asteroid belt. Some remnants of this ocean-dominant world's crust swarm around our sun in the form of comets.
So, on that rare occasion that Earth passes through the tail of a comet, there is a surge of new magic on Earth from whoever inhales/eats/etc. some remnant of the comet's tail dust (including some unscrupulus ones eating someone who had eaten the nanobots... leading to stories like Hansel and Gretel.) The nano-bots lodge in the brain and give access to powerful quantum manipulation devices scattered throughout the asteroid belt that care not about range (quantum entaglement, yo) allowing manifestations of insane power such as energy transmission to cause phase-transition to plasma (pyromancy), opening short-lived wormholes (portals to other planes), partial medical treatment and recompisition of the kinetically challenged (necromancy), etc.
And with only a few bots being enough to trigger, even a dedicated team of autopsists would be confused why people start displaying unique powers after passing by the comet, until a probe goes to analyze the thing.