"Connect via network" wireless debugging not working Xcode 9

I was having the same issue and performed the following steps to get things working:

1. Open "Devices and Simulators"
2. Connect your device and check the "Connect via network" checkbox
3. Disconnect your device
4. Right click listing for your device in the left hand column (Under Disconnected)
5. Select "Connect via IP Address.." and enter your device's IP address

After numerous Wi-fi resets and device restarts (for iOS 12, Xcode 10) I found the solution for me was:

1. Disconnect iOS device from Mac
2. Go to Settings -> Develop on the iOS device
3. Tap "Clear Trusted Computers"
4. Reconnect iOS device to Mac via cable
5. On iOS device tap "Trust This Computer" and enter passcode
6. Go to Device Manager in Xcode and enable "Connect Via Network"

The network symbol appeared and I was good to go.