I've been having the same problem suddenly.
I've had it for a few months, it's been working amazingly. Seriously an amazing machine.
However, yesterday this jumpy thing happened to me as well.
The only thing I can say that I did differently, is that I started using rechargeable batteries for the first time with it, and that I've used 20khz for the first time.
I was also mostly around dry sea sand, it might have got around the coil and is causing problems?
I'm clueless here.