I've had an (almost) identitcal issue for a loooong time, and have put off a new playthrough as I couldn't enter Concord on a new character (but could on older saves). Thanks to your post and subsequent testing, I'm almost certain it's a bug with Preston Garvey. Every time I get near him or spawn him in, my game crashes. For me, it doesn't freeze or stutter, just ctd. Would love if anyone finds a solution to this.