I seem to have a similar fast travel bug that many others are experiencing which will not allow me to fast travel at all, but I did notice something interesting.

When I bring up the PipBoy and switch to the map tab, it often gives me the "unable to fast travel" message without even trying to fast travel. Maybe this detail will help the developers figure out what is going on. I believe this occurred after bringing down the Prydwen. Interestingly, that mission never ended even though the final item is checked off.

Apparently I only used the autosave option since my last manual save was 3 weeks ago when I was 2 hours into the game. This might make me abandon the game sadly.