Hello,
this is my first time trying out 3d coat and i' ve been bumping into the same problem on a particular model i'm working on. After i add some seams, change my uv layout and then press UV Unwrap some areas on my model become grey with no checkerboard projection on them and they also dissappear from my uv set.
I have checked my model and cleaned it up twice by now, making sure there are no weird areas but i have no idea what is causing this.
Any ideas?