Sorry for the late reply.
It either sounds like that the asset is not in the avatar hirachy or VRC Fury is deactivated for playmode. It can also happen if you put it in the wrong part of your avatar like the hip bone for example or if you rename the asset.
Viewing post in Bellyscales for Novabeast (Asset for VRChat) comments
The asset paths error shows up on the prefab before and after I apply it to the avatar hierarchy. I will need a guide on what steps to take to properly apply the prefab. When I attach it to the hierarchy itself instead of attaching to a specific part, the scales and junk show up on the floor behind the tail. It does show it being linked to the hips for VRCFury, though I am not sure if that means anything


