New Recruits achievement not awarded in Assassin's Creed Origins

I have completed the Main quests (including the two DLC) for Assassin's Creed: Origins, so am now working through all the different possible Steam/Uplay achievements. One of these is called "New Recruits" - an achievement that requires completion of two side-quests in the Hidden Ones DLC.

I have completed both of these side-quests, but the achievement wasn't awarded, for neither Steam nor Uplay.

The two completed quests:

The un-awarded achievement:

I've been hunting for some help on this, and found one site that recommended uninstalling the Uplay client and reinstalling it and then restarting the client as well as the Steam client and that the achievement should pop when I restart the game. So I did all this but still no achievement.

Another site suggested cloning my save into a New Game plus and redoing the two side-quests. I haven't tried this yet (this would take a very long time I think), but I will add that the reinstall of Uplay somehow broke my save game and set me back several days to a point where I hadn't done the side-quests on my main save game, so I have just completed them again but still no achievement (which makes me think the NG+ idea may not work)

Is there anything else that can be done to get the achievement to award?

I wasn't sure whether there was something else that needed to be done to make it trigger, so I have completed every side-quest and every location on the Hidden Ones dlc just to be sure, but still nothing.