When i jog the z axis of my lathe with the shuttle pro and change direction, it starts getting to speed then slows almost to zero then up to speed again. if i start again in the same direction its up to speed properly. the problem appends only on change of direction. x axis is fine. if i run a program it does the same thing. i know the problem is not mechanical or electrical. i can see the feed dro following the true axis movement!! it used to work fine. i don't recall having change anything.

any idea?