Lightmap density stretching on some objects

Hey guys I have a strange issue and can’t find a way to fix it.

I have a few object (most of them are like on the image below) where two or more flat planes connect to each other - usually on 90 degree angle but in some cases on a flat surface as well. And in lightmap density preview on one side looks fine but other one is always stretched.

Tried all sort of different lightmap UV layouts (more/less padding between island, different island configurations, etc.) but every time it ends up like this.

And it seems to affect my shadows as well. You can clearly see the shadow (baked from lightmaps) is stretched comparing to the shadow on the other plane.

Any help appreciated.