I just had this problem and thought I was going crazy.
I tried all the above suggestions over and over again.
I finally ended up starting the whole shabang over doing one thing at a time. It ended up it was the tension. It took a couple days. Seriously! I was at it one night for about an hour. the next night for the sam amount of time. I researched everything.
Try doing everything suggested but 1 step at a time. Finally change the tension 1 little turn at a time and it will clean up. Good luck