I don't have that brand of machine, but is the hoop a multi-position? Did
you move it, or have to move it during the stitch-out? If they design isn't
meeting it sounds like it might be a multi-part design which would require
moving the hoop.
I can only suggest making sure the bobbin is seated correctly. Sometimes
just a hair out of position can cause jams because the hook isn't catching
the thread correctly.
Maybe you'll hear from Janome owners soon and they can help you.
Good luck