Janome has been known to have some bobbin issues. I don't think it happens on every machine, but there is definitely a problem somewhere. I have a Janome embroidery machine and have had my machine in the shop 10+ times for the same problem. My dealer tried to tell me it was me: wrong thread, wrong bobbin thread, wrong needle size, sewing too fast, sewing too much, etc. I tried everything and felt I was doing something wrong until I started reading blogs and found that there are a lot of us out there having the same problem. Good luck.