Having only flown in the back & front of helicopters for nearly 50 years, I seem to have missed out on all these jacking problems you guys seem to have had.
The closest to it I can recall is in a Bell 47 & 206 when flying in mountainous areas parallel to a cliff face in very windy conditions, maybe 30 + kts, a gust has hit me towards the cliff face and I could not move the cyclic in the opposite direction. The cure was to move the cyclic towards the cliff to unjam the cyclic and then put in opposite cyclic. Is this what you mean by jack stall? I just considered it as running out of hydraulic control.
I can't imagine this in normal cruise unless you are flying through a massive thunderstorm when anything can happen.