Yeah… same thing happening to me. But with just 1 guild. I have toons spread in 3 guilds in this realm (BanHammer, Wipe Never Ends and Sounds of War), and just the toons in one of them (BanHammer) are bugged. The rest in the other guilds are fine.
same problem here.
My guild is acting weird also. I tried to open up the guild chat on my toon that is the guild leader and I could not it acted like im not in a guild even giving me the option to search for a new guild to join . I can not change guild permissions for my other toons/members. It can not access guild chat its just not there. It does show im still in the guild when I look at my character name. It does still allow me guild bank access. Also cannot invite new members. One of my officers can still do everything just fine tho.
Same - can not see guild members or guild chat. I can see the communities that i am a part of - the members and chat but not my own guild. I am not the only one in my guild with the same issue.
My officer that still had access to everything changed some guild permissions by promoting some members when I was logged off bnet and when I logged back on everything was fixed.
did they do this to the people who were having the issues or just anyone in the guild?
Just anyone. The officer couldn’t change the permissions for me cuz my toon is the guild leader.
Similar thing here.
The guild section is just missing and I can’t talk in guild channels either - though I do see MOTD and my chat addons can see guild members online etc.
ETA: I logged just now and things are back to normal (knock wood). Woo!
Because yesterday I was channeling Karen, I felt the need to also submit a bug report via the in-game system about this issue. (Issue: No Guild roster or G-chat visible, Community Group invisible / issue across multiple toons & multiple servers / Guild bank is still accessible / all toons still showing as in the Guild). I tried a simple UI reload and of course disabled add-ons before I submitted my request. This is the (really fast!) response I got from Blizzard:
"Firstly, let’s perform a UI reset. You can do this by following these steps:
Exit World of Warcraft entirely.
Open the Battle.net desktop app and select the game you want to reset.
Click on the Options dropdown menu and choose Show in Explorer (Windows) or Reveal in Finder (Mac).
Navigate to the World of Warcraft_retail_\WTF folder.
In the WTF folder, locate the “Config.wtf” file and move it to a different location or rename it.
Once you’ve moved or renamed the Config.wtf file, restart World of Warcraft.
This step will reset your user interface settings to their default values. If you’re still experiencing issues after this step, please proceed with the following:
Log in to the game and open the chat box.
Enter the command: /console cvar_default
Press Enter to execute the command.
This step will reset your in-game settings to their default values, which may help resolve any persistent UI issues.
If you’re still experiencing problems after trying these steps, I recommend reporting the issue on the bug forums. Our development team closely monitors these forums and investigates reported issues to provide fixes in future updates."
None of that worked for me. Maybe it will help someone else here. And I figured I’d bump this to the top as I see a new thread about the same issue. Good luck. 
I’m having this issue as well. Server is Turalyon.
I have tried all of the general troubleshooting steps as well.