A post on the official Lord of the Rings Online forums today announced that Troll and Ranger PvMP Session Play will be disabled for the second time. However, unlike last time, we've got a clearer idea about why they are being taken down.
Curse.com's developer tracker picked up on a forum thread where someone was complaining about an exploiting Ranger. Apparently this character was able to reset their Ranger timer to continue playing it as long as they wanted, as well as having the ability to despawn, even while people were attacking, and reappear elsewhere with replenished health. The official response to this post confirmed that the Trolls and Rangers will be disabled due to this.
As a lot of Turbine's staff have already left the office for the holidays, they have disabled the quests for now and will reinstate them once they have fixed the exploits.