My Axolotls keep disappearing/despawning.

I have had this issue on realms as well as singleplayer for a long time now, and i have seen other people on Reddit have the same problem, but no solution.

I keep my Axolotls in a big glass pool. Tons of space, lots of water, no access to land or solid blooks to stand on or get stuck under, no way to get out. I have tried using name tags, naming them while in a bucket, leashing them, breeding them, etc. After some time, they will allways disappear, which really sucks.

It'd be great to get a fix to this after so much time.