The problem with painting the landscape

Hi, I’m making a level, I used to have 5 layers for terrain material, they worked without problems, but I didn’t have 2 more layers, I added them to the material. After that I started painting, everything as usual, when applying a new layer, gray squares appear, but I was surprised that they did not disappear after compiling the shaders. After unsuccessful attempts, I still decided to remove the layer, everything returned to its place, but when reusing the layer, it turns out the same thing. In other sectors, everything is painted well. What could be the problem?