When i try to mirror vertex group in weight paint mode, blender fails with error: "3664 vertices mirrored, 8103 failed". After this operation, the result looks like a mess - sometimes the weight gets randomly sprinkled all over my model, sometimes they stay unmirrored and distort around the area.
I have already performed "Snap to symmetry" in edit mode few times, and blender says that all verts are already symmetrical.
I also tried to do "mesh" -> "symmetrize" all vertices in edit mode. This mirrored existing vertex groups, but after i adjusted some vert-groups in weight painting mode and tried to mirror it - got exact the same error "3664 vertices mirrored, 8103 failed".
How can I find out exactly why the mirroring weight paint fails - i.e. which vertices of my model should i fix and how?
Blender version: 2.83