For instance, the pic provided by the original poster shows a clevis that looks to be about a 3/4" thick with oversize 3/4" holes for a 3/4" pin. A look at Crosby's site will show you a larger pin dia. compaired to the shackels' dia.

If you look at the original posters pic, one of two things most likely happened. Either the pin fell partially out(out of one side), or,  the pin bent which allowed the clevis to expand out until it it slipped off the pin.