The problem you’re seeing is the indirect lighting caused by lightmass.
You can reduce this by going into world settings > Lightmass > and adjusting Indirect Lighting Quality (2 or higher) and Indirect Lighting Smoothness (~0.6). This can help.
For additional information take a look at this thread: Modular Asset Lighting Problem - Rendering - Epic Developer Community Forums
Also keep an eye out on this wiki tutorial for lighting troubleshooting and tips: A new, community-hosted Unreal Engine Wiki - Announcements - Epic Developer Community Forums
There are plans to add this there as well, but that’s at least another week or two out before Eric and I will have an opportunity to get it finalized and up for everyone.