You have a loose wire somewhere, maybe ignition circuit.
I had the same thing happen to my car. Driving along hit a bump on the road ... engine cut out at 60 MPH, freaky! Continued driving hit another bump engine started working again, more freaky.
Continued driving, same process all over again.
Stopped the car, had a look around found a loose screw on the switch-side ballast resistor terminal. Tightened it up, drove away as if nothing happened.
At home I inserted a star washer under screw. No more problems.
It was just a test to see if I was awake. I thought I heard the car chuckle, but may have just been a backfire as I slowed down.
Bob (Brisbane,Australia)
RHD,1967 early 250 SL, auto