How can I set the lightning properly so it doesn't get weird blotches

Hi there,

I am getting strange lightning leaks & shadow moving blotches in walls.

How can I get it working properly?

See arrows on the image:

The general advice for Lumen is to have them as separate independent meshes. Also, it’s recommended to have objects (walls, etc) as 10cm minimum thickness.

it has been exported from twinmotion (datasmith)