How fix the error “loop cut does not work well on deformed edit mesh display”?

I have bought a model on blendermarket. Its a mouth with a moving jaw (so it has an armature)

Im trying to remove a tooth in the mouth, so im closing up the holes in the gum that that leaves behind…
But when i try to add a loopcut… im getting an error

“loop cut does not work well on deformed edit mesh display”

And when I confirm the loopcut…the mesh deformes.

I think it has to do with the armature, but i dont know how to solve it so the loopcut doesnt deforme the mesh and everything stays the same.

Can somebody tell me how to do this? I tried disabling the armature (and deleting it)…but that didnt work…

Sounds llke the mesh contains ngons or tris. And you have a subdiv modifier that causes the deformation.

Turn off the subdiv while you fix the ngons/tris so the loopcut will work, or just manually cut and fill using the knife (on the tool bar) and the fill (F button).