Has this happened after the latest update? I had problems with my Diamond after the update and have rolled the last 2 updates back to before the September one. The machine is now stitching perfectly again.
I was told when I got my Diamond NOT to use prewound bobbins so if you are using one try winding your own-you can wind the thread from the prewound onto a Husquvarna. I did see a differance when I did this.
Humm. I use prewound all the time in my Diamond. Wonder if it's because the dealers want to sell you more bobbins?? Or thread? Guess it depends on how picky your machine is about bobbins?
I believe they have changed the tension system in the deluxe so that may be the reason for the change in use of prewound.
Are you having this problem also in regular sewing mode? I would change the needle and use a new bobbin. Perhaps even use a different spool of thread. Turn the machine off and back on so it goes back to the default settings and try again. Hugs. Nan W
Perhaps the upper tension is now too tight and you need to find the happy medium.