There are many occassions when the Quickbar, doesn't appear, once you log into a server.
pressing Tab (inventory) shows all the binded keybinds, yet once out of the inventory, its invisible, not there. Yet quickbar still usable.

It's an issue that requires you to either relog, or go to the settings, and disable quickbar and enable it again.

If the server is full, and you queued, and you dont know about reenabling it...
I'd imagine it's an unfortunate time spent on queue then relog :)