Modem Puzzle

We have a satellite dish for our internet. We rent the modem from ViaSat. Our smart TV and iPhones and iPad are all WIFI. We also have a booster in the shop so I can stream music. Occasionally our iPhones say no internet connection and we have no service. If I switch over to the extension option it works fine. The smart TV also works even though the iPhone says no internet connection. Any idea of what's going on and how to fix it? Think it's the phone or the modem? BTW, sometimes for no apparent reason, a connection is restored even though I haven't done anything. Thanks for your help.