The bucket of axolotl isn't able to be placed in water for some reason. I did consider if it was the block I was placing it on, which was snow, but it wouldn't allow it as long as there was water already there even after trying another block. It would only place if it was air instead.

If it's not happening if someone tries to recreate this bug, there are two small notes.

This axolotl did have some stuff added to it such as potion effects to stop it from dying if it stayed out of water and a name tag to it, so that might affect it somehow, probably the name tag compared to both. And I did test this in a single player world and it does only affect realms as far as I can see, especially since the other buckets with a fish in it work fine compared to it.