I did think about debris. Today I took all the pucks out, turned it upside down, gave it a shake. Some of the little bits came out. I then had the same problem. After several tries the pucks then advanced and worked properly through the 2 hrs of smoke. Not sure about inside the generator, is there a way to open it up for simple cleaning? The heat plate isn't the problem, pucks weren't even that far advanced and they weren't moving. I thought about puck thickness cause I saw 1 puck in the bag (wasn't in the smoker at the time) that was clearly thinner than the others. Checked the ones in the smoker and they all looked the same to the eye, guess it could be a fraction of an inch and it could cause it to stick.