...once they reach a planet, they do research.
Nope. They're doing research all the time. That's their full-time employment. Aside from the usual time off, it's nonstop research.
Once they reach a planet, they do fieldwork. That means collecting samples, interviewing or observing people, observing animals, taking careful notes and pictures, measuring stuff, maybe running some experiments. Depending on where they land, they might also attend conferences, do guest lectures at universities, workplaces, or for the general public.
Everyone needs vacation time or they burn out, so that's most likely to happen on a planet because, where can you go on a spaceship? You can (and must) have days off, but you can't do a real vacation. So you save it up and go off to some bubble beach and drink margaritas made from something you're going to pretend is agave.
The spaceship is your home base and all your usual work and rest routines happen there. It's where you live. It's where your main lab and office are.
On-planet work is what breaks your routine. In addition to taking a vacation, you're resupplying and getting data and all the other stuff one does with fieldwork. Then you go back home. To the spaceship.
The non-research crew will get some vacation time too and will probably rotate a skeleton crew to watch the ship (if one is needed at all since it will likely get a full maintenance haul-out and a deep clean, though there will be some needed care for plants and animals on board).
Everyone else goes to the planet. Do you really want your cafeteria and janitorial staffs to burn out because they can't get time off from the ship cause they have to stay behind to take care of the scientists? Nope. That's what hotels and dorms are for.
Some but not all of the planets where they stop will have populations. I am inferring that some do because the OP said that some of the crew who did research on planets were sociologists (who study sentient life). Even if none of the planets have other intelligent life (or civilizations) and even if none of them have breathable air, my point about the ship being the primary home and work location holds. Vacations are good for morale, but sometimes they're not possible.
Don't think of planets as places where the "real work" happens. Think of them as the "away" times. The spaceship is home and workplace.