Vertex Group X Symmetry paints both weights onto same area I was painting the weight of one of my breast bones in a rigify rig, with vertex groups X symmetry enabled, and when I checked the opposite bone I realized that it was not symmetrica, all the paint I had applied on the left side for the left bone was also on the left side for the right bone.
I tried clearing the vertex groups and starting over, with the same effect.
The mesh is symmetrical and the bones are evenly placed and named DEF-breast.L and DEF-breast.R
Anyone has any clues of what might be going on?
Can you try to use Vertex Groups X Symmetry without Mirror X.