I am not a FADAL certified repair tech although this has occurred with our machines. You probably have an encoder going out or your amplifier is about to go. We had that problem then it went away about a week before the Vector dirve failed. You may be able to tune the Vector drive and get a few more months out of it. It is not hard. Call Fadal service with your cell phone and have a tech walk you thru the tuning process while you are at the machine.
Jeff Lange
Lightning Tool & Manufacturing, Inc.