In a brief update on the official site, WB Games explains that “certain features” of Shadow of Mordor are no longer available as of January 12 – those will be features like the Nemesis Forge, which allowed you to port your Shadow of Mordor nemesis over to the sequel, Middle-earth: Shadow of War. You won’t be able to pick up Vendetta missions any more, and the leaderboards are “no longer connected to other users” (which kind of removes the point of having leaderboards).
However, thanks to Shadow of Mordor’s final update, you’ll still be able to hunt achievements – even the ones tied specifically to those online features. Repaid in Blood, which requires you to finish one Vendetta mission, can still be unlocked, and so can The Hunt is My Mistress and Lord of the Ring, which were originally dependent on leaderboard scores.