#1 - July 4, 2016, 7:56 p.m.
I believe we figured out WHY it's bugging after some testing today.
In short, we believe it's bugged because of the teleportation of Dalaran. This is how we tested it:
Druid 1: Skipped Broken Shore scenario + teleportation of Dalaran - Artifact quest for moonkin did NOT bug out at Deadwind Pass and was able to continue on to finish it.
Druid 2: Did NOT skip Broken Shore + teleportation of Dalaran - Artifact quest for moonkin bugged out at Deadwind and we could not progress the chain because of a phasing issue.
We repeated this for Affliction Warlock and Unholy DK. Each time we found that the character that SKIPPED the Broken Shore was able to progress while the character that DID the Broken Shore + Teleportation of Dal quest was incapable of progressing.
To make sure this was not simply an issue with any particular player account, two of us replicated this.
For my first two characters, I skipped the Broken Shore and was able to successfully do the Artifact Chain. For my third, I did the Broken Shore and was incapable of continuing. My friend also skipped and was able to continue and then did NOT skip and was incapable of continuing.
If you're one of the players who has been incapable of continuing this - I recommend you do the Broken Shore first and then check to see if you can continue. After, create a new character and skip to see if you continue - if you are able to continue the chain, I'd wager that the bug is happening with regards to the phasing of the Teleportation of Dalaran event.