Follower Spiders "disappear" from chest after changing shards

So long story: Webber with two different parties of spiders - one upstairs, another downstairs. Just finished summer, headed upstairs to the overworld, had some fun, then heard Bearger was coming. Decided to spare at least my nurse spiders so I picked them up and stuffed them all in a chest. Got rid of Bearger then realized I left all my rocks in the caves. Went back down, greeted my cave spiderfriends once again, then got the rocks. Went upstairs for the second time. Remembered I left those nurses in a chest, possibly starving to death. Checked the chest and they were gone. I picked up another random regular spider that was near my base and tried to put it where the nurses were. Spider was successfully put into the chest but then a nurse was in my cursor. I dropped her on the floor and apologized for my misbehavior.

Decided to check if the other slots also had nurses in them and tried clicking on them. Nothing happened. Tried to put another item in the slot they were before and the same thing happened - as if the nurses only came back into existence if I tried to disturb their resting place. Felt bad.

EDIT: Done a few more tests to confirm what exactly is the problem here. I'm guessing this happens because moving through shards should remove the friendship of followers that are too far but creatures in inventory behave weirdly. Tried to replicate this by Disconnecting far enough from the chest but it didn't happen - this might be a sinkhole/stairs only thing.