Steps to replicate

1. Set render distance to the lowest setting
2. Load a chunk in a river/ near shallow waters
3. Unload the chunk
4. All aquatic mobs should have died and dropped their loot

This may have been caused by pairing the mod with entity culling mod by tr7zw:
https://modrinth.com/mod/entityculling

Apologies, after a little testing (and a lot of ram usage) it turns out that it was an issue with more culling and entity culling