Short description of error
Blender 3.0 made disruptive changes without bumping the minimum version requirement.
Exact steps for others to reproduce the error
- Create a file with Blender 2.93, add vertex groups.
- Go in master and open that file and save it.
- Go back to 2.93 and open that file. There is NO warnings yet the vertex groups are gone.
Sample file already saved with 3.0: