firstly would try normal sewing with a different thread. change needle
then would suggest cleaning the bobbin area, then resetting tensions,
I normally set the bobbin tension first then do upper tension to equalise
while realise you may have a more modern machine this info may be interesting
look at page H-3 for the coin method upper right of page
https://www.scribd.com/document/3556...bishment-Guide
good luck

well done for sorting.