A device that is connected to the xfinity wifi does not show in the app

I created a group for my son's laptop on the xfinity app when I first set up the wifi.   I was able to set up a schedule and also I could see the activity on the internet.  However, the same very day the laptop continuously got unassigned. I had to reassign it several times.  Then the laptop stop showing on the app under the connected devices even when it was actively connected to the wifi.  As the laptop is not showing anymore I am not able to assign it to a group, neither to use the parental features nor to pause it.   I have set up today a new router,  I have also changed the name of the wifi and the password.  I have gone to the same setting process in the xfinity app again and things seemed to be ok and then some minutes later I have exactly the same problem again.  Could you please let me know if you have a fix for this issue? Thank you!