Hi!
I use world partition and some time ago I just started having this problem, I don’t know what caused it but my landscape acts wierdly. As you can see from pictures It just chooses to paint specific region while leaving other ones blank, and sometimes it change what parts of the map to paint switching between these two, I don’t know what to do 
You probably enabled/diabled the setting for world orogin shifting.
Regardless of that.
If it keeps happening “randomly” then the only thing you can do is export all heightmaps and layer paint for each level and re-create it in a new folder.
