Check the set screws in your pulleys to make sure they haven’t loosened up. Check your eccentric nuts for tightness.
Many have experienced this type of problem when the spindle (if you have the 24 volt 300 watt) is getting ready to die. Increased electrical noise from the spindle can cause missed steps on the stepper motors.
its probably the stock spindle get a new one of get rid of it. once it starts going our it sends RFI to the steppers due to the higher amp draw to make it spin. RFI stands for radio frequency interference. i found a company that sells shielded stepper motors that i intend in buying when i get to upgrading that part to insure that it cant happen to my machine. they are also water and dust resistant built and mend for the food industry.