This user seems to have had a similar issue:Issues importing FBX Animations (inverted limb rotations on UGC bundle rig with additional joints)
Basically, when importing animations through all import methods (import queue, animation editor, blender animations plugin, importing from roblox via id - even older animations are inverted) the animations have completely inverted rotations, becoming unusable.
I tried every method to import them but none work, even uploads uding asset IDs of animations which were imported before and used to work normally on the same rig i am trying to put it on.
The issue mostly happens on GLB rigs although i am getting it on FBX too!
Expected behavior
When importing a custom rig with an action, all rotations in the action/animation become fully inverted and practically unusable.
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