All good points made here. It’s true that it is possible to jam a Schweizer type release if the load is applied in the wrong direction, perpendicular to the long axis of the swinging link. Denny made a great point about the tow plane being susceptible.
I also wonder if the pitch attitude of the kiting glider rose to a point where the angle of the tow rope caused its release, also, to jam.
In essence I wonder if both releases jammed at once because of the unusual pitch attitudes.