I don't have any luck quilting with 100% cotton bobbin thread. I use an all purpose or poly and it seems to have fixed the problem. Also, make sure your bobbin is going in the right direction. Lastly, there are at least two clear plastic bobbins, one is flat and the other is slightly rounded. If I accidentally use the wrong bobbin, I get this too. I wonder if it's the minky... I would try a poly thread if all else fails.