Going on about 10 hours with this bug and wanted to throw it out to the community before I submit a bug report.
On my particular mesh (attached), Blender handles the shapekeys just fine. Everything that is supposed to move, does.
However when importing to Unity about half of the vertices are “locked” in position while everything else moves. It looks terrible. See photos.
Changing Unity Normals to Calculate “fixes” the issue of vertices not moving. Unfortunately this is not a solution for me because the shaders I use bug out majorly with calculated normals. I need Import normals just like on my other 50 or so models where it works fine.
Things I’ve tried:
Deforming the mesh shapekeys (Transform, Scale, Rotate) in blender then exporting to unity
Copy and pasting the vertices and deleting the old ones
Copy and pasting vertices in to new projects
Mixing new shapekeys from existing shapekeys
New unity project
Hours upon hours of google searches
You can open the attached unitypackage and see for yourself how the verticies locations change significantly depending on imported or calculated normals.
I am also having this issue… Not sure how barely anybody has noticed it. Everything looks fine in Blender, but I have the same issue as you in Unity.
Unity seems to be defining a threshold under which vertexes don’t move in a blendshape. Or maybe it’s a threshold built into the FBX?
If I uncheck Legacy Blend Shape normals on the FBX import in Unity, and set Blend Shape normals to Import, this issue goes away in the FBX but when I export it to a VRM the issue shows up again.
