Fort Independence is the ONLY place I have had this problem with, in 130+ hrs of play on this game, so I doubt it is a driver/CPU/memory issue (though I have had other crashes, this is the only persistent one.) If I do not approach the Fort I am fine.
I am running a couple of well-used mods from nexusmods - FWE and MMM, but as I've been to Fort Independence fine in the past, I doubt they are the trouble.
I notice the Brotherhood patrol that spawns on the west side of Fort Independence is stationary, and Defender Rockfowl and Defender Morgan are missing from their posts but alive if I move them to me. Moving these NPCs (including the patrol) doesn't seem to make any difference. I can get much closer to Protector Casdin from the northeast; if I try to approach from the southwest, I start crashing in the hills before I get to the Fort.
I have read through many bugs around Fort Independence but haven't seen anybody who cannot reach the Fort at all.
Thank you for your attention!