Character Can't See NPCs or Other Players in Main City

This happens when a character starts the Broken Shores quest chain and never finishes it.

If you pick up where you left off and complete it through Illidari Allies (Alliance) or Keep your Friends Close (Horde), you'll be phased back into the normal version of Stormwind or Orgrimmar.

Current Quest chain for Alliance:

1. The Legion Returns
2. To Be Prepared
3. The Battle for Broken Shore
4. The Fallen Lion
5. Demons Among Us
6. Illidari Allies

Current Quest chain for Horde:

1. The Legion Returns
2. To be Prepared
3. The Battle for Broken Shore
4. Fate of the Horde
5. Emissary
6. Demons Among Us
7. Keep Your Friends Close

There is actually a legal way to skip almost the whole quest line till some stage. If you already completed the whole invasion quest line on at least on character before, your other characters can skip from the first 2 quests. If you just completed The Legion Returns and/or To Be Prepared, you still can skip next steps by talking with your faction's NPC:

• Alliance - Recruiter Lee
• Horde - Holgar Stormaxe