I have been having an issue with my wireless card for a while now. Sometimes when I boot into my computer the WiFi doesn’t work. In the network applet it will display the wireless card and underneath it just says ‘disconnected’ in greyed out text. To fix the issue I usually just reboot but recently I have had to completely power off the system at the plug to make sure it will work again on boot. The system can recognise that the PCI wireless card is there but for whatever reason it cannot search for a network, let alone connect to one.
The card I am using is the TP-LINK TL-WN851ND with the ath9k driver.
04:03.0 Network controller: Qualcomm Atheros AR9227 Wireless Network Adapter (rev 01)