Which drive system does it have (Electronize, 4QD, Armortek silver box) ?
Which RC system do you use (Futaba 6EX, 7C, Spectrum) ?
How is the receiver powered (battery, BEC, Armortek PSU) ?
It sounds like the receiver is losing connection with the transmitter and the in-built "fail safe"system is cutting in. On an 'plane, this cuts the throttle but on a tank it puts one track in reverse, hence spinning the tank on the spot.