Everytime I move / modify / undo my geometry, the engine starts "Rebuilding BSP"

This just started happening a week ago. Before that it was fine. I was adding new geometry, subtracting from existing and had no stutters / latency whatsoever. Now all of a sudden, everytime I modify any geometry the editor freezes and tells me its “Rebuilding BSP”. This has never happened before. I don’t even have that many geometry instances in my level. The “Update BSP Automatically” option doesn’t help because it simply allows me to move the geometries’ wireframe around so I have no idea how it looks in the editor until I rebuild. Is there any reason this would be happening all of a sudden when it wasn’t happening before? Thanks.

Edited - It says “Rebuilding BSP” not geometry.