Ever so often my Janome will do that. The upper thread jumps out of the path - I don't know how it does it, or why, but it does. (Usually when I am in a hurry.) And even though this machine has been with me for five years, I still keep the manual near the machine to check back and make sure I have set the tension right, or double check the path. I have even missed a step threading the bobbin. (I have 3 machines that I use regularly and all three thread differently.)
A friend of mine called me once because she was so frustrated with her embroidery machine, the thread kept breaking, and I asked if her thread on top of the machine was in the right position, (laying flat or or upright if it on larger thread holder) and that was all it was. She sews a lot and other machine it makes no difference but on the embroider machine it does. I sewed for years on a 15-91 Singer, and it made no difference which direction the bobbin went in. I was amazed that it mattered on my new machines. And I think it was this board that pointed it out, I joined after buying my Janome with the drop in bobbin. I took the classes and learned how to put it in, but ever so often I thought it was misbehaving and it turned out, I had put the bobbin in wrong.
Good luck, I hope that it is just user error and nothing serious.
Last edited by quiltingcandy; 12-17-2016 at 11:19 AM.