Could be a number of issues:
-Belts too loose OR too tight
-Pulleys slipping (check setscrews are tight and one is centered on the flat on the shaft)
-Pots are too low OR too high
-V-wheels are too loose OR too tight
-There’s probably a couple more things I’m forgetting at the moment
Easiest way to troubleshoot is to start off by checking the pulley setscrews, then the V-wheels (barely moveable by finger). If you want to check your belts and pots, I put videos on how I adjusted them on my machine at X-Carve Maintenance/Troubleshooting Videos - Add Your Own!