What's the issue you encountered?

Fabric 0.15.11
1.20.1 MC Version

[10:26:47] [main/WARN]:
Reference map 'graveyard-FABRIC-fabric-refmap.json' for graveyard-fabric.mixins.json could not be read. If this is a development environment you can ignore this message

[10:27:00] [Render thread/ERROR]:
No data fixer registered for graveyard:reaper
[10:27:00] [Render thread/ERROR]:
No data fixer registered for graveyard:acolyte
[10:27:00] [Render thread/ERROR]:
No data fixer registered for graveyard:corrupted_vindicator
[10:27:00] [Render thread/ERROR]:
No data fixer registered for graveyard:corrupted_pillager
[10:27:00] [Render thread/ERROR]:
No data fixer registered for graveyard:skeleton_creeper
[10:27:00] [Render thread/ERROR]:
No data fixer registered for graveyard:falling_corpse
[10:27:00] [Render thread/ERROR]:
No data fixer registered for graveyard:ghoul
[10:27:00] [Render thread/ERROR]:
No data fixer registered for graveyard:revenant
[10:27:00] [Render thread/ERROR]:
No data fixer registered for graveyard:wraith
[10:27:00] [Render thread/ERROR]:
No data fixer registered for graveyard:nightmare
[10:27:00] [Render thread/ERROR]:
No data fixer registered for graveyard:ghouling
[10:27:00] [Render thread/ERROR]:
No data fixer registered for graveyard:lich
[10:27:00] [Render thread/ERROR]:
No data fixer registered for graveyard:skull
[10:27:00] [Render thread/ERROR]:
No data fixer registered for graveyard:nameless_hanged

How can the issue be reproduced?

Unclear how but i assume it might be tied to Better animations collection, Fresh animations, Entity mods used for fresh animations.

Logs

No response

Additional information

Grave stones work fine so i'll keep it on but i don't see any added mobs. but thats fine to, i prefer just having the tomb stones for making bone armor. if you'd like you could make a light version that's just tomb sites and basic zombies and skeletons. might be more user friendly for a lite version.

update 1: i finally did encounter 1 mob the accolytes in the abandon mansions.