Zbaitu M81-FF80-EAIR X-axis lagging issue

Something mechanical is wrong in the X-axis.

Turn the power off and slowly move the axis by hand. Look and feel for anything binding or sticking or loose or interfering with smooth motion.

This discussion, although it started from a slightly different symptom, covers pretty nearly all the things to check:

You should probably check the Y axis while you’re in there, because it may develop similar problems.