Same issue to me. It was caused by this giant blocking volume I was using as a Sketch for rebuild the entire level with static meshes. Removing the volume now it’s calculating at normal speed. So if you have this issue, try to work in a temporary level without strange volumes on scene, or bake to static mesh as many geometries as possible.
You can also make a copy of the level, remove a part of the geometries to work faster, and then copy paste to the “original” level. There are many workarounds.