Realm: Azjol-Nerub (EU)
Currently have an issue where It appears that guild chat and officer chat have vanished, however GMOTD, guild list online and offline notifications are all ok, even getting guild member achievement notifications, but guild chat and officer chat have vanished.
It is working for some but not others
more people are having the same issue.
I am also having the same problem all guild and communitie functions have stopped working even calander stuff for all our raids has gone
Had the same issue, Before I was disconnected and now cannot log back on lol
Guild chat is also not working anymore i do not even see the guild tab.
i do see people in the guild and chat.
Same issue for myself. Only way i can see who is online in my guild is if i do a /who on it. other than that no guild chat and nothing else at all for guild
Great, so its not just me then. Just joined a new guild and couldnt see the chat or the member list, but the tag above my head is there. Hope they recognise the issue and fix it soon.
Its okay, guys. It was just me looking for RP communities. Everything will normalize soon. Stay tune! 
It’s because they made the decision to tie guild chat into the new communities window, which in turn requires battle.net. Whenever battle.net has a connectivity issue you can’t use guild chat.
If you just want to see who is online you can use the /groster command but you can only converse using whispers.