I'm going to say it's your battery. Checking the voltage without a load doesn't tell you much. Could be something as simple as a bad cell in the battery.

You should try measuring the battery voltage and the individual cell voltages if you can, while you put a load on the battery. Could be as simple as several automotive lights.

If you drive your buggy slow for several minutes does it happen? If not, that would be another indication of a bad battery.

The only other thing I could think of is a faulty receiver. Had a receiver that would loose signal and would cause the car to be unresponsive for a couple of seconds, then would come back to normal. Rebinding the receiver to the radio fixed that.

I was able to confirm it was a lost signal by keeping an eye on the LED on the receiver. When it lost signal it would flash.