Here is a way to determine whats going on. With unit parked, hitch locked ready for travel and hooked up, raise the trailer using the front jacks until the king pin starts to lift above the saddle. Continue raising until it starts to lift the truck. You should only have a 1/4" to a max of 1/2" gap if I remember correctly. Anything more than that you have a hitch issue. Its probably the locking jaw bending upward. What appear to be happening is your gap is big enough for the saddle to tip downward and allow the wedge to jam up an out. Make sure you have the correct wedge and that is is as far froward as possible in the saddle opening.
@SteveCass From you photo it sure looks like you ended up high hitched. Is the jaw still around the kin pin shank, and not the end collar? Looks scary as heck.

Not trying to over think this, but a heavy spring on the back side of the hitch to keep the saddle tipped up might help