The motor encoder is basically a feedback encoder. In the previous post, I told you about checking the tension device and standing on your head to check it. My memory was faulty. What you need to check is the nut on the gearbox drive shaft, if it is loose it causes all kinds of problems, some of them are as you described. And that is where you have to stand on your head to check. Sorry it has been a while and the memorys fade.