Since you have a simple I'll rule out all dual extruder classical issues.

I think you can have this happen inn case of over extrusion : the head then keeps bumping into the print and either the print unsticks or the belt skips. You can usually notice it because the noise is very distinctive from normal operations.

Another thing to check is that both Z axis move evenly : I once saw a right Z coupler slightly untightened and the gantry could not lift evenly. It was barely noticeable at first. But since you are talking about X axis I think it is relevant as the gantry is on X axis.

Finally, have you tried to :
- home XYZ, perform G29 and then move the head around by hand with motors disabled on control panel.
- re-home XYZ, re-perform G29 and move the head around but with control panel this time.
- lift Z 10mm, move around and check that you have 10mm everywhere.

What is PB support saying on this ?