I've had this exact same issue. Every now and then, the servo would work and the car would be ok, and then all of a sudden, the servo would not work. Sometimes the whole car, esc and everything would shut down. I tried using a receiver capacitor, aka Glitch Buster, and that still didn't work.

Turns out the wires inside the servo were torn and were no longer connecting with the servo board. It would also short itself, which was causing the random shut downs.

I resoldered the wires to their respective slots and everything is perfect.