I have a Brother Runway Edition. It was doing the loopy thing. After trying everything else, we unscrewed the cover for the top & found a small piece of thread. Once this was removed, sewing was back to normal. We used a piece of dental floss to find the thread. It was black, which I love to stitch with since I like vibrant, strong quilts, but was basically invisible when it was caught up in the machine.
Good luck!