I'd first check the machine mechanically.
X or Y axis slides and screws have not gotten tight, dry, dirty, sticking or dragging.
Couplings, shafts and pulleys are all tight and secure with no slippage.
Do multiple rapid moves to a dial indicator or accurate reference point to check closely for any missed steps.
As machines get used, their characteristics can change due to the above factors and sometimes require a clean-up/lube job or a re-tune of the motors.
If missed steps are suspected, reduce the max speed and acceleration by 50% and try it to verify, then tune up for best results.
If it worked well before, and you changed nothing, my guess would be mechanical.
Good luck,
Russ