Huge FPS drop in any underground area

Since the Devblog 97 update I can not go near anything underground. This includes Caves, Water Plant, and Tunnels. If I enter these areas, or get close to them (in the case of the Water Plant), I drop to 1-10 FPS from 100-130 FPS.

I have tried lowering my settings, following some FPS guides, turning Virtual Textures on/off. Nothing seems to work.

I had hoped this would have been fixed with this update, but it seems it was not, and I am unsure as to what to do. It makes it very hard to enjoy the game when I am limited to where I can go.

If anyone knows a fix for this, please, let me know. Otherwise, please Facepunch, fix this.

Known problem.