Walls turn black at an angle.

I made custom materials for my map, edited the vmt to make it vertexlitgeneric, and then added them to my map. It’s just a room with a light in the middle. When I go into my map though, if I look at a certain angel, the walls turn black. I say it was something to do with my vmt but I’m not sure. Here’s a video showing my problem:

Any advice helps.

Vertexlitgeneric is for models.

And all model textures when applied to brushes turn black at certain camera angles ingame.