Boolean glitch

Hey all. I recently started using boolean to do simple mouths on my characters. When I make the characters all works fine. But when I start animating sometimes the object with the boolean modifier disappear for a frame, than come for a few frames, and repeat. I know its not lag, as I looked through the animation frame by frame and it still happens. The only fix I’ve found so far is rotating the head a little until it becomes visible again, but this is kinda annoying. Does anyone know how to fix? Thanks!

No, it’s not a lag. It’s rather automated triangulation of the mesh (mess) left behind the Bool operation. Sometimes triangles can overlap without your knowledge.
IMHO you’d be better off using proper mesh modeling, V to rip edges, Shape keys for vertex groups.