Creality K1C - XY shift during print

I’m having a strange issue with my K1C. During the print, the printer suddenly loses the correct XY position and continues printing from a completely different XY coordinate, while Z continues normally.

The print doesn’t stop or show any error. It simply shifts the XY position and keeps printing in the wrong location, ruining the part.

This happens with models sliced by me (Creality Print/App), while the factory preloaded models print perfectly every time.

Has anyone experienced this kind of random XY shift? Any idea if this is firmware, slicer, motherboard or stepper related?

check belt tension… I had this once, one of the belts was loose…

Thanks! I’ll check the belt tension.

In my case, the strange part is that the printer suddenly shifts the X/Y coordinates during the print and then continues printing normally from the new position, without any error or stopping.

Interestingly, the factory preloaded prints never have this problem and print perfectly. The issue happens with other models that I slice myself.

How did you tension the belt in your case? How did you determine that the tension was correct/adequate? Is there a specific method, measurement, or reference you recommend for the K1C?

Thanks!