Weird Shadow artifacts

Hey!
I have a problem…
So i have no Idea what causes them. they just once appeared after a light bake and I am at a loss. There is no geometry that should cause them. The windows are two planes. One with a cutout shader for the Iron parts, the other one is a translucent lit one. The bakes before it worked without a problem.

I use mostly static lights. The blue light comes from a stationary spotlight from outside and casts Volumetric Shadows. The wall allows volumetric translucent shadows so the shadow of the window is colorful. (check the pictures for details)

I am using the UE4 on 4.25.1