Building lighting freezes my engine... This fixable?

So I been working on a level and everything was working fine. But just the other day I added some level BPs and 2 mesh pieces and all the sudden when building the lighting the engine freezes. I thought it was the BP warning I got, I fixed it and nothing. I can build the paths, LODs and geometry one by one with no problem. But once I select to build the lighting the engine freezes. I’m using engine 4.12