I have this problem too. After I get the warning that the bobbin is almost out, I watch really close and stop the machine just the minute it gets caught. If I don't it affects the bobbin case and I've messed up 3 or 4 and had to buy new ones. The problem is with the little end thread that is first wound on the bobbin. it starts getting stuck and the machine tries to use it as well as the thread it should be using. If I am machine embroidering, whenever it tells me the bobbin is about out, I immediately put in a new one and use the small ends for straight stitching when I can watch and stop it the minute the little end starts to get caught up with the other thread. This happens with the prewound bobbins as well as the ones I wind myself.