And this only happens, if you start a print? "Home head" from the menu works normal?
What about the gcode file? "front and center" sounds like it is not prepared with Cura / UltiGCode? Are you printing from the sd-card? Perhaps you've just changed anything at the start-gcode (accidentally)?
And yes...: which firmware version?
Did you install new firmware? Please update your profile to indicate you own a UM2.
If you accidentally put the UMO firmware on the UM2 that would explain the problem.
Try fighting the head during homing. If it seems weaker in one axis than the other then probably one of the 4 wires going to the stepper is broken. The most common place for a while to break is under the metal covers in the back corners which come off with only one (or two in some models) screws.
There is a DIR (direction) pin/signal that runs from the arduino chip to the stepper controller chip. So either the arduino could be bad, the PCB trace, or the stepper driver. The trace is very unlikely. The stepper driver is more likely.
You can reverse the two wires in either pair to the stepper but don't do that because I suspect it's the DIR pin and the head will keep moving always only in one direction and reversing the wiring will just make it always go the other way.
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