The two chickens in the picture I've posted are stuck on stop of a chest, but underneath a block. I don't know if it's specifically the Sea Lantern that causes it or that any block would cause it to do that, just that it has to have 1 block space above a chest. It's not a duplicate of MCPE-49607 because mobs will stop trying to go wherever they were going when they get hit. These chickens did absolutely nothing. It also happened with a fox I had roaming around.