You did say if you were sewing versus FMQ. If FMQ, your pressure bar has to be lowered. A lot of folks miss this. (ask me how I know) Also your thread on the top of the machine has to be in the take up lever. If your thread is slipping out of the take up lever, it will cause this problem. These two things normally cause what you are experiencing, unless there is a burr in the bobbin area keeping your thread from slipping off of the "appendage arm". Hope this is fixed for you soon.