I am not familiar with the Maxilock thread you are using--what weight is it? I only use an 18 needled on the long arm when I'm using something that is a #30 or 40 weight thread. Do check the bat as Paper Princess says, some definitely have a right and wrong side.
Really wish you had a picture so we could see; but I'd suggest you change needle size and also experiment with differnt bat or switch sizes. Sometimes when I pop my bobbin into the machine I have the thread tail get wrapped around something in the bobbin case and it will stitch fine on top for a very short distance and then get "stuck".
I'm also wondering if there is a timing issue? I'm not familiar with the Janome tech system, but think a phone call to them is warranted if these things done help. and get some canned air and really clean out that bobbin area, too.