Hello,
I saw your post and wondered if you had figured anything out about your machine? I am having the same problem. I am on my second brand new machine from Amazon and the same thing is happening. The first machine worked for 3-4 weeks then the speed started varying and the thread cutter would engage without prompting. This second machine, which I have had for 2 weeks has started doing the same thing. I can get about 1-2 hours then it starts doing the same things. Can you pass on any advice? Thanks