Bug description: "The player will be unable to access Railroad HQ where Desdemona is, if before siding with The Institute the player has already started the quest Tactical Thinking from the Brotherhood of Steel. The secret passage will be locked, and the player will not be able to interact with the mechanism to open it."

When you're given the "Tactical Thinking" quest, the triggers to BoS soldiers Spawning at Old North Church, as well as the Secret Passage to lockdown are instantly activated, and even if you change your faction to The Institute, the BoS soldiers will spawn, and the Secret Passage will still be closed, but the triggers for the detonator won't start (as you're obviously no longer in the BoS, this is the correct behavior) nor the ability to interact with the button to activate the secret passage (this should start, but it doesn't, because the passage shouldn't be actually locked), and thus the player is unable to finish the quest, and is completelly locked out of the Railroad HQ.

Can't get any more specific than this, please Bethesda, fix this issue as it is completelly game ending and it's freaking urgent and the fix is quite simple, just add a trigger to allow the interaction with the button if the gate is closed and the player active quest is End of the Line, not Tactical Thinking.