Many years ago the animation editor didn’t have rig validation. It is now outright rejecting rigs that previously worked fine. This loss of backwards compatibility should be classified as a bug because it is an unexpected breaking change and completely blocks developers on formerly valid and often very complex rigs.
I have many old rigs I’m backfilling emote animations for. These rigs were created before we had robust tooling for making avatars; many are handmade or hand-modified, so they do not follow perfect conventions. It’s currently impossible to use the animation editor for them anymore because they have duplicate part names on detail parts that are not animated, or unusual Motor6D hierarchy. I am now stuck with rigs that I can no longer work on animations for with the Animation Editor, and to get them to work again, I have to do significant surgery with trial and error, sometimes breaking many animations that already work fine depending on the nature of the issue.
The animation editor should handle these rigs that fail validation differently. Never ever ever outright block the user unless the state of the rig is completely unworkable. It is not sensible that the tool is blocking users on rigs that worked just fine previously, not every rig issue constitutes a critical failure.
Instead warn the user that parts with non unique names cannot be animated. Provide better information to help developers find motor6Ds that are affecting the same part. Help them fix it in a way that won’t break previous animations. Have nondestructive failure modes that allow the user to still load the rig, load animations on the rig, and use as much functionality as is reasonably possible.
This is a big reason why users are turning to tools like Moon Animator.