I was sculpting the terrain and mountains on separate layers, but when the mountain layer is active, the material is partially stretched. The terrain is a smooth hill, and the UVs are not stretched with height. Clearly, distortion occurs where the terrain and mountains are painted at the same time.
In the first place, it is nonsense to paint differently using sculpting layers. There is already a layer for painting. Why do sculpting layers influence painting? It’s really annoying…