Was still happening on Beta in the last week before Early Access, so I better post it here in case they delete the “In Development” forum soon:
When players complete the Alyza Bowblaze story quest (“An Orphan’s Request” [79151] beginning in Mereldar), she will join them during the “Pool Cleaner” WQ (so no risk when you didn’t do that story quest).
When WQs become available with the leveling campaigns completed) and you’re on this WQ, Alyza has a dialogue option to send her back to the orphanage and some players might be tempted to do that.
On Beta, instead of making the orphan disappear when the “Fine. But you better kill lots of kobyss for me.” talking was done, the players were put into a phasing of Hallowfall with almost no creatures, etc. and this affected the whole Warband!
If you’ve sent her back (and got phased out, otherwise no one cares) this script should return true on all your characters:
/run print(C_QuestLog.IsQuestFlaggedCompleted(82131))
Potential way to fix Hallowfall, and I hope it will help you as well!
- Go back to Hallowfall and find the orphanage building (the script will create a link for a Map Pin when you copy it into your WoW chat.
/script DEFAULT_CHAT_FRAME:AddMessage("\124cffffff00\124Hworldmap:2215:4179:5578\124h[\124A:Waypoint-MapPin-ChatIcon:13:13:0:0\124a Alyza Bowblaze Map Pin]\124h\124r");
- Walk up the stairs where you should see Alyza Bowblaze. Talk to her and use the “You can join me in the Hungering Pool again.” gossip option.
That’s it! A very simple solution for a severe issue when you have no idea what causes it. Took me several weeks to find the actual reason while I was waiting for a fix that never happened.
Good luck and have fun with all these savage creatures thirsting for your blood again! 
