I was having snarling problems with my Singer a few years ago. Looked at the bobbin and learned that the millimeters difference and being concave (convex? can't remember the proper direction) versus flat really did make a huge difference in how the machine worked. Of course, I wasn't smart enough to toss or at least mark the ones that don't work, so I had to do a test run last time I pulled out that machine.
Cheers, K