A similar thing happened to me during the heli training activities. I realized there was a default binding that was setting the throttle to zero.
Hmm, that sounds plausible. On the other hand, it happened four times to me, in similar situations, so it is unlikely I’m hitting a particular key. But still, maybe I did. I’ll review the bindings and see if some key is assigned to “set Throttle to zero”. Reviewing/managing key bindings on XBox is rather cumbersome (I’m envious of players on PC 
)