iOS 18 Wifi Issue - Unable to Send/Receive

Ever since the iOS 18 update, both my wife's (iPhone 14) and I (iPhone 16 pro) are having issues with wifi in our home. None of our kids (3) are having issues, but they are still on iOS 17.6.1.

Problem: The phone remains connected to the router, and shows full "wifi bars" but you are suddenly unable to send or receive data unless you turn wifi off and use cellular data. A phone restart, reset, reset network settings, etc does nothing, you cannot get internet. The only thing that seems to work is to reset the modem/router. Again, no users on iOS 17 are having issues here and we have fibre GIG internet, we had no issues with the same devices prior to upgrade to iOS 18.