Another issue is roll, if the truck or trailer "roll", and the other vehicle doesn't (it only takes a fraction of an inch) the wrong way, the king-pin and be a little bound against the mechanism that you need to release the king-pin.
Normally all you have to do is put the landing gear down, start the truck and put the transmission from park to neutral and back to park.
I see this most often when say the trailer is level and the truck is slightly pitched.
I also see this more often with my PullRite then I did with a fixed hitch
Under the worst case I have to un-pin the hitch head from the truck and use the landing gear to raise the head off the truck, this finally releases enough tension on the king-pin.
Oh, ya, I think to off-straight number for the PullRite is 15degrees.