Thanks for the update. This is really a puzzle. Hope your dealer can get this resolved for you soon.
Are you using the correct power cord for your machine? Is the dealer using your power cord and/or foot pedal? Try a different power cord and/or foot pedal. They may to be need replaced.
Do you have directional sewing on this machine model? It lets the stitches sew at an angle or other direction rather than straight. Check the preference page screen for settings if you do. They should be in the default setting which has a black box around the number.
Next suggestion: Does your machine have Memory Pockets? These are places to store a favorite stitch so you can use it next time. Do you have any stitches in the pocket?
I finally found the update for you. Here is a download for the update on your machine. It is not hard to do yourself. The steps need to be done in a specific order. The dealer should be able to do this for you if needed.
https://support.brother.com/g/b/down...00eus&os=10014
Good luck!