I have 2 Janomes, both computorized. I hardly ever use the button that does the 3 stitch end/ beginning tack. The one time l tried it, l found l must've accidently programmed a " start" and "stop" length of stitching , resulting in what you are experiencing. Maybe you accidently selected that button instead of the 'reverse 'or 'cut'? If you turn it off, rest for 10 seconds, it will hopefully forget the command. If not, try unsaving it ( check manual).