While running this task, the second step is Recover pages from Evylin's journal (4). The mobs that drop the pages are unattackable, a sol'dal archivist.
Did this on AB 2 days ago without any issues, also seen other guildies later that same day get the achievements. Server issue maybe?
Having issues on other Argin Hiz tasks as follows: The Keeper's Ring - Chunk of Solenium from Laborers in mine is not updating task when looted. The Reclusive Collector - Ember Hunters/Huntresses stopped dropping fire peppers after 4 were obtained. I overcame this because suddenly the spiders at entrance started dropping peppers. Bristlebane server on 7/25.
I was able to complete Rings of Fire today with no issues on Bristlebane. I was also wrong about the The Keeper's Ring problem described above. I didnt realize i was looting Selenium Ore rather than Chunk of Selenium, which does in fact update the task.
Still having this issue on FV server, we have tried this multiple times, and everytime it breaks at this same spot. We cannot fight the a Sol'dal archivist mobs need to move forward
Was able to confirm this and it is now being tracked internally. Thank you for your report! Until a permanent fix can be made, it should be possible to avoid the problem by waiting an extra 60 seconds before hailing Vasser Faveil after zoning into the instance.