Please try the steps given below and check if it resolves the issue:
1. Hold the power button on the console and wait for it until it shuts down and then reboot the console.
2. From the settings go to "Network", and hit "Go offline", wait for a minute switch back to "Online" then re-launch the game.
3. Turn Xbox and router completely off, wait a minute and turn on again.
4. For advanced users who are able to reset router settings: Turn off Xbox, turn off the router and reset router settings. Turn on again.
Please let us know if the issue persists. We are always here to assist you.