I'm thinking that there is so much rigidity in the body,,and the fit and finish is so tight that there is no place to go except the apex of the triangle (two door hinges,,,one door striker mount)which is probably flexing just a few thou enough to bump the mechansism onto safety latch position.
I think you are on the right track with turning a few thou at a time off that striker pin until the problem goes away.
at least it's the cheapest probable fix