Bobbin & thread problems

Check the stitching and confirm that it is in fact bobbin thread and not the top thread that is creating knots & loops under the fabric. This is usually the case and is called thread nests or bird nests. (You can search the internet for more information about this symptom.)

Install a brand new needle.
Remove the thread from the machine.
ALWAYS RAISE the presser foot while rethreading the upper thread.
Confirm the thread path is correct.
Verify the bobbin is installed facing the correct direction in the bobbin case and the bobbin case is threaded properly.

Set the upper tension to the midway point (factory standard) although it may need to be tweaked as machines change with use and time.

Pull up the bobbin thread. This method works with general sewing projects, not just quilting.
How and Why to Bring up the Bobbin Thread

Begin to test sew slowly.

If the thread is still making a mess, then the machine most likely has a timing issue. There are multiple web sites and videos that discuss sewing machine timing. Or take it for service.

...

1. Replace thread with good thread. (Check by holding to light to see if there is fuzz).
2. Adjust the bobbin tension. The tension on top is set to three and the bobbin tension should be equal to this amount.
3. Replace needle.
4. Check the top tension with tension foot down to see if the thread can move or does it get stuck? If it gets stuck the tension control may need adjusted or cleaned.
5. Pull the bobbin thread above the throat plate and pull on the thread. It must have some tension but not get stuck.
TENSION TENSION TENSION IS THE PROBLEM!

can't figure out what you mean, what bobbin seat, do you mean on the bobbin case? maybe on the post where the bobbin case goes? I guess you just have to work on getting the thread off and start over.

Try these suggestions
1. Change the needle--use a needle that's for the fabric being sewed
2. Rethread the machine--top --make sure to use every thread guide
3. try a different bobbin--make sure bobbin is inserted correctly into the bobbin case, & make sure the bobbin is turned the correct way in the bobbin case
4. make sure the thread has not come off the thread take up lever
5. Clean under the needle plate & in the bobbin area for lint or threads

The needle thread breaks
1. the needle thread is not threaded properly
2. The needle thread tension is to tight
3. The needle is bent or blunt
4. The needle is incorrectly inserted
5. The needle thread & the bobbin thread are not set under the presser foot when starting to sew
6. the threads were not drawn to the rear after sewing
7. The thread is either to heavy or to fine for the needle


Bobbin thread breaks

1. There is a right way & wrong way to insert the bobbin in the case --when you insert the bobbin in if it doesn't stitch correctly turn the bobbin over see if that helps or bobbin case is not inserted correctly

2. Lint has collected in the bobbin holder

3. The bobbin is damaged & doesn't turn smoothly

4. Lower thread tension is two tight

I suggest to change the needle anyway, the tip of the needle could be
damaged
clean under the needle plate & in the bobbin area for lint & threads
rethread the machine top & bobbin

try changing needles
clean under the needle plate & in the bobbin area for loose thread or lint
make sure the bobbin is inserted into the bobbin case correctly--if the
machine won't pick the thread up from the bobbin correctly take the bobbin
out of the case & turn it around & try it that way.

have you removed the thread so the bobbin case can also be removed
to check the bobbin case & see if it's damaged or has any burrs on it

try changing the needle
clean under the needle plate & in bobbin area for loose threads & lint
try rethreading the machine top & bobbin, make sure to get every thread guide
make sure the bobbin is inserted correctly in the bobbin case

It sounds to me that you might have the wrong type of bobbin in the case. The top of the bobbin should not be higher than the case. Thread will slip through the space and cause problems. Also unevenly wound bobbins will also cause this symptom.
Or your losing tension which you will have to adjust tighter.