Not a long-arm story, but recently I was doing free-standing lace embroidery and thought my machine needed service, or even replacing. Thread was shredding every couple hundred stitches, and I had a dozen leaves to make at about 12000 stitches each! I did all the usual stuff—changing needle, adjusting tension, running some monofilament through to see if anything was caught in the system—and still had shredding.
I then tried putting a thin line of Sewer’s Aid—the silicon stuff in the little plastic bottle—along the thread on the spool. Problem solved! Worth a try, maybe.