I had a very weird problem with my Galaxy Tab Pro SM-T520. After working fine for a while the tab suddenly was not able to see any wifi network. None of them. Not mine, not from my neighbors, just the whole Wi-Fi networks list in the Connections Settings was empty and the "Scanning..." process was hanging.
Reboot the tab, on\off, etc. the wifi did not help.
Only the factory reset did help. However after some time the same problem came back :(
It has happened after the WiFi network was disabled for a while. Android 4.4.2