Hello astronaut61,
In order to better understand this issue I would like to gather some more information from you.
1.) What is your lightmap resolution set to?
2.) Can you link a copy of your DxDiag?
3.) Do you have your engine scalability set to epic?
I will also link you to a troubleshooting guide for lighting. If you are still having this issue after providing this information and looking through our troubleshooting guide I will continue to assist you in solving this problem.