Is it repeatable? If not, consider what's changed from when the fault was apparent to now - moisture, etc.

Almost certainly electrical noise, poor earthing, or inductive coupling (or, more insiduously, hardware failure exacerbated by those).

Try, if you can, swapping the X/Y axis feeds to confirm that the problem follows the change (so that the X-axis moves, not Y) - that will tend to isolate the problem to the control box. From there - don't know your machine (other than it's chinese) then look into the control box to check the integrity of cabling to the stepper driver on the faulty axis, and the cabling from the BoB to the driver. Check supply voltages are common, try - if you can - swapping suspect for working drivers (again to localise the area of problem). Pay attention to the feed to the spindle, and how this is routed near signal lines - look if you can provide separation or screening. Check that the spindle feed is shielded and that this is earthed with a star topology with the rest of the control electronic supplies.

A photo inside the control box would be interesting.