I've experienced a scary issue when re-importing my skeletons' JSONs onto my Unity project.
It makes the SkeletonDataAsset inaccessible...:
This was after changing the names of some animations, which happened to have Custom Mix Times configured on the SkeletonDataAsset...:
(this is how it was before the first re-import attempt)
So, I needed to rename those animations back to their original names, reimport, delete those custom mix times, change the names again in Spine, reimport, and the it was fine.
Now I need to reconfigure those mix times, which is not a big deal, but I was wondering if this something to expect, or a very specific bug.
If it's the latter, then here's my report. :p
Edit: my versions are Spine 3.8.99, Unity 2019.4.9f1 and its Spine runtimes 3.8-2021-04-02