multires modifier and unwanted creasing


I have a student who is having trouble sculpting this hand she created. For some reason, when we add a multires modifier to the mesh the areas around the knuckles collapse. I’d love to know why this is and how we may fix it.



hand2.blend (634 KB)

The mesh is non-manifold. There are edges connecting the surface through itself and also a face connecting to a wrong point. Should remove those until the mesh elements define a surface like it was a glove made with 0 thickness material.

Selecting none, select menu -> select by trait -> non-manifold helps to find problem areas.