Strange lightbake behaviour

I can’t figure this out:

When lighting baked:

When moved the lights:

It behaves like it should with the green light on the back (same blueprint setup just different color parameter). Both walls are simple BSPs.

Is your lightmass importance volume covering both lights and all the meshes?

Yes it is.

I recreated that wall now and it bakes correctly now. No clue what could have gone wrong, I left the settings of the BSP untouched except changing the material. One other annoyance was that I also had to recreate the subtraction volume since it didn’t subtract anymore. Bake works also with the subtraction working now.