I've lost the connection to a single device, what should I do?
This could have happened for a variety of reasons. It could be a specific service going down, you moving your device out of wireless signal range or having that signal interrupted by some sort of interference.
The first thing to do is ensure you are within range of the router or access point(s). If the Wi-Fi signal is strong, turn the Wi-Fi off and then on again on your device. If this still doesn't work, try restarting the device as this may allow it to reconnect.