If your Xbox One and SmartGlass app aren't working well together, here are some things to try.
In the router settings, turn off isolation mode if it is enabled. Make sure your device and console are not on the guest network.
Some wireless routers have a feature called "wireless isolation" mode, "guest mode" or something similar. This allows devices to have internet access but not to communicate with other devices or computers on the network. Xbox SmartGlass cannot automatically find the console, and even using the IP address does not work.
If you have a dual-band router, make sure that you have different SSID names in your router settings. This can simply mean adding a “5” at the end of the SSID name for the 5ghz range. Ensure that your devices connect to the proper SSID.
Some dual-band wireless routers allow you to specify the same SSID for both the 2.4ghz and the 5ghz bands, and some do this by default. When the SSIDs are the same, routers can have issues routing traffic correctly on the network. This means your devices and console appear to have internet access but devices will not connect to the console.
If none of the other solutions have worked, then try this. You might need to reconnect your wireless devices to your network afterward.
Follow the steps in your router manual or manufacturer website to reset the router to factory defaults. Connect your console and device to the wireless network before re-establishing your security settings. Tap the Connect icon in SmartGlass and connect to the console. Re-establish your security settings.