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Instead of a keylock style hitch pin use the appropriate sized bolt with a nylock nut and washers.
Even if they are carrying 2 spanners make sure there is plenty of thread sticking out so they get bored before they get the nut all the way off.

You can see the pin is still in the hitch, the big black lump is the load transfer mechanism.
the receiver tube has cracked off around where it is welded into the cross-wise tube.

My vote is a combination of bad welding on the hitch (undercut) and overloading due to the load transfer mechanism. The way those bars twist the hitch to force the front wheels of the car into the ground is an unnatural way to stress the tow hitch, it's effectively putting the underside in tension. The hitch is designed for a given amount of "pull" and a given downward force on the tow ball.

I bet they didnt engineer it to be pushed down and also twisted upwards. Anyone from a tow bar company able to provide some info?