Just to add to this report.
Bonebrah sent me one of his models and I spent the last hour trying a whole manner of things to see what could be causing the error. (I get it too on my end).
At first, I thought it was animation related, but that was a red herring in the end...changing animation names doesn't require the mesh to be rebuilt and thats where the issue comes in....when voxels are added/changed
In the end, two key discoveries were made I think:
1) I deleted all voxels and frames (empty mesh) and saved the model...still get the same error
and
2) bonebrah made a new model and copied the voxels/frames over and that one saves without issue.
Trying to do Save As...
just recreated the same issue in the new file.
Both would lead me to believe something has gone awry with the core .scn file somewhere/somehow
Now it would appear the file is not corrupt or bad as there's no major impact to the game...model still loads fine.
But just unsure what could be causing this issue with the file itself.
Bonebrah is understandly not too keen on opening 100's of models, to create new ones and copy frame by frame over lol
The issue doesnt seem to be impacting things though thankfully, but just wondering if there's something you can spot that might be causing it with this file (attached), or at least confirm if the issue is something to be concerned about.