Hi, It is only happening on the back. I can tell something is off though because it will start to sound funny. The top thread looks wonderful. Yes, we have rethreaded multiple times and after we rethread it it goes back to sewing fine for a while and then the loops will start happening again. Every time after this happens the thread is still in the tension disc and spring. We've used new bobbins at 180 with So Fine. I'm using a panto that has constant changes of direction so it's hard to tell if there's a particular direction. It has also happened all throughout the quilt so no specific place. Thanks for your reply!