Having had 3 ZEDs I have found that once the tyres get below 3 to 4mm of tread on the rear, and I suspect whatever they are, given the 4 types I have used, that as the roads currently are even a light right foot will spin the wheels, not helped if the tyres have not got up to full operating temperature.
I also think it is probably a case of learning the 'limit' in adhesion that only time with your 370, given what you have said about your confidence level, will tell.