Painting a Fog/Lightning Layer - issues

I’m trying to paint a fog/lightning layer. And on most spots, it works fine.
However there is one area (maybe more in the future), that seems to have an invisible wall that wont let me paint it. Additionally, I get this wild spikes at one specific spot as well, which also doesnt seem like this is supposed to happen. Anyone happen to know what causes this, and if so, how to fix it?
See the picture below. The unpaintable area is half of a 64x128 tile.

Different mod, different tile, similar issue, except this time with the terrainbrush. I was able to paint terrain on it before. But as I tried to brush it up a bit, patches of mud on the road etc, I noticed a certain area wasnt working. To find out the exact area, I used a 50 M brush radius and turned it into grass, except for the blocked of area, which for whatever reason turned black. [Edit] I’m not using custom imported brushes or assets or anything, just the base GD stuff.

[Edit 2] I just closed the map without saving. Tried again, I could paint that spot, initially. Then after fixing the terrain elevation again a bit, I couldnt paint it anymore, but a different blocked of area this time.

Whenever i run into problems, the first thing i try is to re-build the map (both Rebuild all pathing and Rebuild all maps).
If there are still glitches in the Editor, i come out and rebuild the maps in the Asset Manager.
These have always solved the map creation problems in the Editor for me.

I tried quite some of this. Heck, the tile is so bare bones I just removed the region and made it a new. It fixed it, for the most part. But there are some specific spots where it just keeps happening. Not sure why but with enough re-do’s I’ve got some of it working :smiley: