I too have a Xerun v3.1 I find throttle cuts out when your ESC is too hot, motor is heat soaked, battery is low, battery doesn't have enough C rating.

I think the more real culprit is your battery not being able to put out enough amps for when you are pinning the throttle. You get maximum draw when your trying to move the car from a stand still. A higher C rating battery, 50C or higher will help.

Also when my batteries are near the voltage cutoff I will periodically get a blip in my throttle when I am pushing the motor hard. For instance, from a stand still or right out of a tight turn.