It sounds like you may have static building up in the bobbin. A couple of things contribute to this... Long periods of time operating... the constant spinning of the bobbin can have static build up. The second contibutor is poly or poly cotton thread in the bobbin. The spinning coupled with the poly will can have a signifcant amount of static.
I would try , test a bobbin with just 100 percent cotton thread and then the bobbin washer to see if it continues.
This may be the issue , not having seen the issue first hand this is worth a try to trouble shoot.