I’m experiencing problems with precomputed light on a landscape:
As you can see, there are visible seams right at the boundaries of the terrain segments (next screen is from the landscape mode with a terrain segment highlighted):
It happens only at this particular area, which is occluded by lots of static meshes (like a cave). It looks ok on the rest of the map and on the other maps as well (with identical settings):
I’ve also found out that this artifact is caused solely by sky light (turning it off fixes the issue). There are only a directional and a sky light on the map, both of them is stationary.
Here are the world lightmass settings:
Landscape light and lightmass settings:
Sky light settings:
I’ve tried tuning different settings, clearing all the cached lightmaps and rebuilding light with max quality, but this bug just won’t go away 
Would really appreciate any thoughts on how to fix this.