Strange npc flight bug.

Hello.

I am having this strange bug where I try to take the flight from the npc in Dalaran to Sholazar. Once I accept the flight prompt all npcs, players, etc. vanish and I am not sent away on the mount. See video here: https://files.catbox.moe/wujxsw.mp4

I have noticed this happens with flightmasters too sometimes, and other similar quests. I have tried disabling all addons but it doesn't change anything. Simply relogging helps, all the npcs and players come back. I have tried abandoning the quest and picking it up and trying again but to no avail.

Anyone know anything about this?