OK so I've just finished and turned in to missions for the Railroad. When I get the (way to brief) pop-up to defend Tenpines Bluff.

I pretty much drop everything and head outside, hoofing it. I'm not even passed Bunker Hill about 2-3 minutes into my journey when I get the Failed, pop-up. WTF?

So I re-load as I make it a habit to quick-save right after I get a defend settlement X quest.

This time I fast travel... (urgh I still feel dirty, I hate fast travelling.)

So a bunch of Synths have spawned and are all pretty much standing huddled up together inside the settlement, fight lasts 5 seconds.

But the quest never resolves. I skirt the perimeter to scout for stragglers, but there are no enemies left. The quest auto-fails if I stray too far from Tenpines Buff.. so what gives?

Has anyone else run in to this problem? What's the solution? Just let it fail and move on? Even tough I didn't fail at al? (well the game forced me to use fast travel, so that's a failure right there)

Just had this issue today. Found sometimes if an attacker is killed outside the build zone, then it doesn't trigger mission complete.

If on pc, try dragging the corpse of any outside the build zone into it, resurrect through the console and kill them again.

Hopefully, this is one that gets fixed.

Cheers! that did it. Since it was a Synth attack, I threw the traitor's body of a cliff... Had to haul it back up to resurrect but it did the trick.

Now I just hope that the ultra short respond time was also a bug, I don't like to be forced to fast travel.