Hi Joseph,
It looks like you have 2 layers to the mesh (an outside and an inside)
Perhaps all the outside verts are weighted correctly to the Spine bone (at least I think it’s the spine)
But those verts on the inside are weighting to a second group that they shouldn’t be.
Try looking at the weights in weight paint mode and/or click on those verts in edit mode and look in the ‘item tab’ which will tell you what groups the active vert is weighted to.

Hope that helps.