I might have missed something but just in case I didn't ... if the fore end sits central in the channel after making those wrist face adjustments described, imho, the next place I would check is the inner recoil lugs to make sure there is equal and even bearing there. If the wrist face is corrected , then it seems it would be easy for one of those inner lugs to have lifted off. I assume firing in this condition would hammer the one high one until they evened up, or manifest a noticable issue.
Perhaps Peter will comment.