Are you using the same power cord and foot pedal at home? Change location of the power outlet.
Did you try a pre-wound bobbin in your machine? They are always wound better. Check to make sure you have the right bobbin case and correct bobbin. There is a case for bobbin work that may have come with your machine accessories. Did it get switched for the regular one?
Do you have a preference page on your machine? Check that all settings are in the default setting first.
Are you using straight stitches or decorative stitches?
Are the feed dogs set for sewing or FMQ?
Does your machine have all the "updates" installed? The dealer should be able to tell you the latest update. It should be on the machine site for support. These are free to download and install. You can check your version on the preference page on your machine.
You mentioned thread. What type of spool is the thread?
Such a puzzle. Can you post pictures of good/bad stitches?