Missing faces problem

Whenever I would try to make a cone with more than 11 faces at this certain scene I'm working on, some of the cone's faces would disappear. Whenever I would copy-paste ANY brush from that scene into a new scene and try to make the cone again, same problem happens. But when I would try to make the cone in a totally new scene or in other scene's I've finished in the past, no problems occur.

Anyone know how to solve this?