sometimes the thread can get wound on too tightly or loosely or crosses over itself which will cause problems. do you have another bobbin you can try? or take the thread off and re-thread the bobbin.

are you using bobbins that came with the machine, or are specific for the model? different machines can have slightly different sized bobbins and if you get the wrong ones they might fit in but not twist smoothly leading to issues.

there are heaps of points on a machine that can be adjusted that can make big differences. getting the machine serviced might help get everything tightened properly.

hope you get answers soon