I'm finding out that some machines are much more sensitive to threads than others too.
This new Singer caused me no end of trouble this afternoon. It was most likely something I did, but at this point I don't know what.
The thread wadded up in the bobbin area and my wife had to dig it out with tweezers. Some pieces were the thick C&C jeans top thread and the rest was the thread I've been using the last couple days.
All I was doing was trying to make a button hole.
I'm pretty sure much of the problem is the damaged bobbin carrier too. Next week I'll have to order one in.
Joe