Unfortuntately, Arch doesn't support the TP-Link
TL-WN823N by default, so you have to install the drivers by hand.
If you're using
netctl to manage your network connections on Arch and need to connect to a hidden wireless network, make sure that you have
Hidden=yes in your config file e.g.
After upgrading YouCompleteMe recently, it stopped working. My first thought was that the libraries needed rebuilding: