Lately my Dolphin Triton attempts to climb past the water line, suck up air then freezes at the bottom. Takes a few seconds before it moves again until the next climb. Therefore losing the capability to scrub along the water line. I always clean it good after each use and stored in the garage. No sign of external parts degradation. My take is that the impeller is pushing it too hard against the wall.

I searched but doesn't look like a common problem. Anyone?