When you say "all the rest" do you mean decorative stitches? How does a blanket stitch come out?
Suggestion #1) Does your machine have a usb port on the side? Make sure you have the latest update for your machine. You can check what version your machine is on on the preferences page.
Suggestions # 2) Take the sample with you to the dealer so they are sewing the same sample.
Suggestion # 3) Do you have a lock button on your home screen? It allows you to lock a stitch in so you don't accidentally change it. Make sure it not in the lock position.
Suggestion # 4) What bobbin are you using in the machine? Be sure that you are the recommended size and type. I use Fil Tec size 15 but check your manual. I also use pre-wound bobbins as there is more thread on them. But don't REuse to REwind other thread. They are meant to be thrown away when done.
Ask the dealer to contact B*rother with the issue as there may be a pending update. Perhaps there is a re-set the dealer can do. They need to see the issue in order to fix it.
Do you have the option of either sewing or quilting buttons on the initial start-up page?
Take pictures of the screen button and how it stitches so the dealer can compare them. Hope you get the issue worked out soon! It's hard to go without our machines.