HCA: Hermit Crab Association

So I know what you're thinking "hermits are social and like to be together" but I'm curious if they may have difficulty breathing.
So My isopod colony, when I first started, was gathering to the top of the lid. I learned it was from a lack of ventilation and adjusted the container.
So I have a level very close to the top of the tank. They love it, but why are all my crabs piled up in the corner in a plastic plant? They have been very inactive for a little over a week. Of course I've seen them each roaming around, but them being so piled up in a corner concerns me. Then again they could be just sleeping together or such.
Tank: 20g high
2 small PP, 2 medium PP, and a "sorta" jumbo. He's pretty small
Imagine a well setup tank, I've got it
De chlorinated, both salt pools. Etc
Thanks

I'd add a picture but I have no idea lol

They do sleep in huddles and hangout close piled up

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My guys love cuddling in the shower caddies I use for shell shops and spend most of their down time up there when they aren't eating, drinking, etc. I've always just assumed that being up off of the ground is an instinctual safety thing for sleeping/chilling out during the day. Cuddle piles are normal, and adorable too! I think it's mostly a social thing, but probably a bit of the "safety in numbers" mentality as well. My guys think they're clever camouflaging themselves in the shell shop I don't think you have to worry about air flow as long as there's a little ventilation, or if not, the top is being opened a few times a week.