I just noticed huge fps drops at the end of Bunker hill battle, after you free the synth and get out of the basemant.

I was hanging around inside Bunker hill settlement looting corpses when fps dropped from 60 to 15. There were inside the settlement few Raildoad NPC floating midair frozen in the crucifixion posture and Vertibirds flying in the background. Maybe vertibirds were causing these fps drops?

I had the same drop again not this drastic though in another place just before a Vertibird was about to start crashing.