Hello!
I had this problem too, I couldn’t submit my changelist in source control because of this. The way I was able to “fix” it was by disabling “Edit Layers” in the Landscape. Your landscape will stay the same but all edit layers and all the references on the layers will be gone. I guess it works like “Flatten” in Gimp or Photoshop. It’s not really a fix for people who need to keep their landmass brushes though or the edit layers themselves.
Hope this helps someone. 