If anyone is having this issue in 2020, here’s what fixed it for me - I wasn’t able to save my level, builtdata.uasset was coming back as “unable to save due to partially loaded bla bla”. Removing all lights and newly-added actors didn’t help, neither did fiddling with lighting manually and clearing all bugs. But deleting levelbuiltdata.uasset and letting level build one from scratch seemed to work. So if you’re having this issue, you can try this sequence; 1. remove all lights from scene if you can 2. make sure absolutely no other assets are saved in your folders with same filename as asset you can’t save, ie. level file and builtdata file for me… if there are, rename/delete dupes 3. back up your builtdata.uasset file 4. delete it 5. rebuild level lighting
Pretty sure this all happened because editor crashed in middle of a light build.
Good luck