If you’re seeing the warning for "Lighting needs to be rebuilt! (x unbuilt object(s)) then you should use the console command for DumpUnbuiltLightInteractions and then open up the Output Log Window to see what actors are listed for causing the unbuilt lighting issue.
This is the first step in tracking down what your issue is. From there you can investigate the offending object(s) and correct the issue so that it doesn’t become unbuilt or doesn’t need to be built for static lighting.