Yesterday my mask didn't work and I dont know why. When I saw my character in Moho he still looked okay but when I rendered him out the strokes on his tshirt - which I drawn with mask technique seemed have no masking effects at all. I created a new file and draw other 2 circles masked each other and it worked fine. Any idea?
Impossible to tell without seeing your layer and masking setup. It doesn't look like a nested/complex masking setup, but if it is, the workspace will not show the correct final results.