Cannot modify or delete mesh without it collapsing I've been working on a model for a game, and found out about Shape Keys for clothes/armor that can be changed out. When I tried to squish the torso, I found out I can't scale it at all. Then I found a rip in the mesh - which is strange since its from an applied mirror, and the cut isn't on the other side.

It turns out this cut has to be from Cthulhu or something, cause it completely wrecks everything.

https://youtu.be/XbFRfi2QcJM

I made a video showing what happens if I duplicate the other side, or delete the vertices around it. It just goes berserk and collapses on itself.

The only modifiers on the effected mesh are smoothing and armature.

Does this mean it got corrupted? Is there a way to stop it from becoming a black hole and devouring the entire upper torso? Or is the only option starting from scratch?

Edit//
The Upper Torso shape key likely needs to be removed, or at least you need to disable the Shape Key Edit Mode option