Light bleed using Lumen

Needing some help. I’ve searched all over and can’t find a fix or even a proper explanation.
When using lumen to light my environment, I get absolutely horrendous light bleeding through my walls. I have attached pictures to show.

Couple things I’m not understanding:
1)
The light bleed only occurs on actors that have been merged together. Example is in my picture. The walls on the left have a wall segment, and a trim segment that have been merged. You can see how the light bleeds through.
The walls on the right have the 2 segments (wall and trim) seperate, and there is no light bleed at all.
What would cause this and/or how would I fix it?

If I left all the actors as merged, how would I go about stopping; or blocking, the light bleed on the other side? I will say that I’ve made sure everything has shadows enabled.
I have seen other people suggest making another mesh and then checking the “hidden” option and that would create an invisible wall that blocks light, but that does not work. As soon as it’s hidden the light shines completely through again. And yes…shadows are all enabled on the mesh too.
Another person suggested making mesh and unselecting “render in main pass,” and that it would also leave an invisible wall that blocks light. But again…this does not work either, because clicking off “render in main pass” still leaves a big black block where the mesh is, and if I check the option to hide it…then the light comes right through again as if nothing is there.

Someone please help. I have spent 2 full days trying every single thing I can and trying everything that others have said work, and they don’t seem to work any longer in 5.1



From the pics it looks like the wall pieces sit exactly snapped on the floor, correct? If so, what happens when you turn off the snapping and “bury” the walls in the floor a bit?

Thank you for responding. Doing that didn’t change anything. I rebuilt lighting too just to be sure.