Try a bobbin check, and rethread.
If that doesn't work, unthread, and walk away till tomorrow.
Rethread in the morning. I have gone to my repair person for the most ridiculous reasons. 911 calls....
She tells me most calls are 95% operator error....
Wrong sized bobbin, (the two machines I have, are not bobbin compatible), needle in the wrong way...
OH VEY!
Six ways to stupid, I've done it all!