I'm not entirely sure if this is technically a bug, but some mobs easily get stuck on chains and they can't seem to pathfind off of them. They have to get pushed by other mobs or I have to push them myself. Axolotls might get off of them if they target a fish.
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GoldenHelmet
The issues shown in the screenshots are not specific to chains. They are issues rather with mobs that hover and swim. Resolving as a duplicate of MCPE-61625 and MCPE-39073.