If the problem is intermittent and you have replaced the ADON Board, I think you should check the Brakes. You should have 1/4 inch of thickness on the linings, and the Flat Washer under the center adjusting Nut should be movable by hand. Perhaps someone puts a heavy load on ounce in a while and you are slipping through the Brake. Putting a full load on would be a good way to see if you are holding with the Brakes. It is also possible you have gotten a bad ADON from Spares. A not unheard of scenario.