I have a strange problem with my mesh. I modeled a low poly character and used the rigify plugin to generate my rig.
Now when I try to move the mesh with the base rig shape, some vertices are staying on their position. Here is a screenshot. I am note sure where the problem is!?
It’s not a strange problem. When you use automatic weights, you get a good result, but not a perfect result. There is almost always some clean up to do. After you parent your mesh to your armature, you are supposed to make extreme moves like that, so you can find those errant vertices and fix them.
The problem is this: there is a mesh vertex group (same name as the bone) that should include those non-moving vertices, but it does not. Find the vertex group the vertex is supposed to be in (usually a close by bone), select the vertex, and assign it to that vertex group. You can do this in edit mode, with the vertex group panel visible in the Properties Editor, mesh tab, or you can use weight painting.
You will probably also find some problems around the neck and head area, when those bones are rotated, and maybe around the hip joint.