@jamesbriggsy I'm also in the same predicament.

@ubi-mark It seems restarted my game solved the issue - whatever issue it was. I was returned back to before I started the mission, just outside the raid area.

@ubi-mark I thought of that too. I went by boat, road, did a whole new side mission to see if it would catch up to itself. Nothing's worked. I'm currently standing next to Reda's shop in Dublin. I'm going to try to go to sleep once I find the tattoo "shop" to see if that will help. I can't meditate or fast-travel to England. I'm stuck. As a last resort, I may restart the game.

@mabelleame EDIT: It does this for any of the missions it seems. So I can't complete "War Efforts".

I've killed the person and left the area, but when I leave the area it says that I must be anonymous, and yet I wasn't detected at the time. I went back to see if I needed to loot anything from the NPC but they were no longer there and I ended up becoming detected and getting damage. I can't complete the mission no matter where I run to (since fast travel is locked) because the game doesn't recognize I've completed it, so I have the message "You must be anonymous" stuck in the middle of my screen even when I change missions.
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@jamesbriggsy I'm also in the same predicament.