Welcome to the forums.
I've never heard of that problem, but it is just a piece of stamped sheet metal and when its donor rifle got buzz-sawed it might have been torqued/rotated/turned/IDK (a shame, since it was never a machine gun, but the great emperor ATF the magnanimous dost make his rulings). Literally, have you tried just flexing it the opposite direction with a pair of gloves on? That might be all you need. My guess is that the neck area got turned somehow, and this is reflected in the rear. Just grab the neck and the rear and turn the rear in the direction opposite its mounted state while turning the neck the other direction (as if you were wringing out a wet rag). Don't go nuts with it, just flex it a bit and see what happens. A little at a time and you may have what you need.
Rise of the Dark Son - by Davis E. Riddle
Fiend Fighter - by Davis E. Riddle
Skein of Shadows - by The Wandering Men (member, Davis E. Riddle)
“A citizen may not be required to offer a good and substantial reason why he should be permitted to exercise his rights. The right‘s existence is all the reason he needs.”—Judge Benson E. Legg