Issue #25296: Speak to McCready misc objective
First time you enter the third rail one of the npc tells you about mccready and a new misc objective shows in your pip boy - talk to mccready
Then you enter the room where he is at and the whole scene with the gunners play out and you choose to recruit him as a follower or not
But the objective to talk him will only be marked as completed once you recruit him, and that can cost you 200 caps at minimum. So if you don't want to recruit him the objective to talk to him will still be hanging in your quest log even after talking to him proper.
As a contrast, the misc objective to "explore the combat zone" is marked as completed right after you enter the interior, requiring no "exploration" at all
I know this is more of a OCD of mine than a bug proper, so I will understand if you ignore this