My belt driven Scott Sub 10 slips teeth under really high torque. I dont know if this is typical of all belt driven, but they seem less robust under torque genrally.
You should check the tension of your carbon belt. Gates has an app to help you do that. Usually is just a matter of loosening the back weel bolts, adjusting the screws that push on the axel and retightenig the weel. If your frame doesn't have the adjustment screws you should check your bike manual.
I got one of those! I've done most of my commuting on it during the past year. Mine doesn't slip under load. Perhaps check with your bike shop that it is tensioned enough?