Home Network Issues

I'm hoping somebody can explain what is happening with our network and how to fix it  - in plain English, please, as I am not highly technical. We are constantly getting "no internet" messages on varIous devices, even when there is internet on other devices. The setup is this - Xfinity modem with 2 extenders and a mesh extender we just added. So we have the main network - myname, plus myname_2.4 myname_5.0 and the mesh network also myname. We stream all our tv and have laptops, tablets, phones, etc. Tonight I could not get an internet connection on the main network even though I am in the next room but I could stream tv on myname_2.4 and also get that one on my phone and laptop, albeit very slow on the laptop. The Xfinity app kept telling me it was restarting my modem, but I was still watching tv, untIl it actually did restart. I always have connection to the network but not to the internet, even though there is still an internet connection to the modem at the desktop which is direct wired via ethernet. I hope that is enough info for someone to tell me what is going on and what to do about it.