I have never ridden a ST2 - but I've been riding my ST1 for over two years. On mine the rear brake will cut off the power so yours being out of adjustment can cause what you describe. Another thing I've noticed on mine is if I put pressure on my peddle while I am powering up my bike it will sometimes feel like it's not right - all I have to do is turn it off and turn it back on making sure I don't apply pressure on a peddle while it starts back up and it runs perfect. Your bike is under warranty so they will replace the rear wheel/motor and the display if that is the problem. It sounds like the people that are trying to fix yours don't really know what they are doing.