I have the 4.0 and the Performance 5. What mode do you use? I much prefer the Sensormatic. Does your machine do it in all modes?
I had a really frustrating day at a quilt class last year when my 4.0 simply would not FMQ for any length of time - thread breaking continuously. I changed to the Spring Motion mode and it worked fine. The next day I gave the bobbin etc. a good clean and it worked perfectly again.............
If you haven't already watched
Superior Threads video about thread and tension, then I'd thoroughly recommend it. I was amazed by just how low the top tension had to be (ignore the Auto tension setting on your machine - threads vary so much, even within weights - e.g. two strands or three?).
I haven't come across loose bobbin winding before, but I'd suggest the next time this happens you take the machine in and ask them to wind some bobbins to see if there's any difference.
Btw - adjusting tension was a revelation to me. Before my Pfaffs I had a mid-range Janome. That machine FMQ'd with anything, including metallics! I can't remember
ever adjusting it's tension (mostly because as a new sewer/quilter I didn't know how, lol). Ah! The bliss of ignorance!