I have a similar problem with a 27" PBG baritone neck. I believe my specific issue relates to moisture in the Lab and incorrect storage of the unfinished neck (It was bolted up to the JM body I'd made leaning against a wall for a few months). I'm going to see if I can clamp it to some known straight surfaces and correct it.

I'm glad to hear yours has stabilised somewhat @GeraldL.