A couple of years back, my new SM parts supplier sent me a sample of some pre-wound bobbins. I tried them out in my Pfaff and the upper thread started minor nesting and bottom threads started breaking.
What the heck?
I tried about 3 times and gave up. I was in a hurry to finish something and tossed those bobbins in a drawer.
Fast forward a couple years now, and my long arm arrives. The dealer swears by pre-wounds (tension, volume, etc...) I'm skeptical, but I figure I'll try them in the LA. She loves them except one particular one. As soon as I put the bobbin in and start to stitch, she starts snapping the thread and I'm getting a little nesting again.
Since it's a practice day, I'm not in a rush. I investigate and find that the bobbin she's complaining about is slightly overfilled. One of the winds had puddled off and wrapped around the spindle that the bobbin case sits on.
I removed about 10m of the thread, put it back in and stitched until the bobbin ran out. After that, I tried them in my Pfaff too and it loves them, as long as the bobbins aren't over filled.