My Bernina Artista 730 does the same thing. I had it in the repair shop, and they told me nothing was wrong with my machine, and nothing could be done.
Someone told me to start using leaders and enders. But that's why I paid for an automatic thread cutter! I have since moved on to using a Babylock machine, with no problems using Aurifil.
If you find a solution that works, I hope you will post it. My Bernina just sits waiting to be used....