This happened to me striped down the machine and gave it a very good clean. It was full of furry bunnies every where .
Gave it a new needle and changed the type of thread and started again. Also checked to see about oiling. One drop of oil wiped around bobbin casing and wipe needle.practise on spare material as oil may leak.
Clean down the two slits in machine top if you can a feather is useful. This may solve the problem as the bunnies get everywhere.