DEUF Refabricated is a fabric port of the mod DEUF (Duplicated Entity UUID Fixer) by CAS-ual-TY. It fixes duped UUIDs, removing log spam and also fixing some crashes.
This mod only needs to be present on the server to work. But it's recommended to be included in modpacks to fix these issues while on singleplayer.
The entities will only be fixed on spawn, which means that if your world already has duplicated entities, this will not fix it, you'll have to remove them. Future entities that spawn while this mod is installed will not be duplicated.