I can't figure out what's causing it, but I have not been able to create an impostor of my avatars for a while now:
(avtr_3460b0a5-b357-4fe5-a670-59c08f135083) &
(avtr_aec76abc-33ec-4513-8c5e-6dd37c5ed4b4).
They have started to fail impostorization after the open beta update where VRCHeadChop was introduced (1431). Before that though, I was able to create an impostor of them just fine.
So far I have tried:
  • Uploading without VRCImpostorSettings, VRCImpostorEnvironment and VRCHeadChop components.
  • Uploading to a different Avatar ID.
  • Removing all custom Animators, Params and Menu.
  • Removing all particle systems.
  • Making sure the mesh is humanoid.
  • Creating a new project without any custom packages.
Before it used to say "An unknown error occurred", but now it says "Failed to create Avatar Impostor Prefab".