Possibly lost steps.
Check the machine mechanically (pulley set screws, belt tension, eccentric nut/V wheel adjustment) and verify that all wiring and connectors are in good condition and secure.
Best check is power up, connect to the machine, go to Settings | Debug and then jog to the center of movement for each axis, installing a probing pin along the way if that is an option, then grab the tip of the pin (or the shaft of the spindle) and try to shift things in all directions — it should be rock steady, if not, investigate and address.
I always advocate for calibrating for belt tension (once one has it set well), but that shouldn’t be necessary for most folks: