No internet but WiFi stays connected

Wifi shows no internet connection every other hour or so. To fix the issue, I have to disconnect from currenty wifi network to another on the same router. Problem occurs again after another hour or so...etc

It seems that the connection is still there as I checked from dos window with ipconfig/all but I could not ping out to google DNS server 8.8.8.8 for example 😐

Am using a Netgear AC1900 router. I reset the modem through the Xfinity app support line but issue came back after another hour or so again. I called the Xfinity support line, they ran some signal diagnostic test and they indicated that nothing is wrong with the signal...etc By the way, this issue also occurs while connected through ethernet cable directly on the router so is not a wifi issue.

Anyone else having this issue or can share any other info that may help please ? Unfortunately there is no FIOS in my area but am searching for other options to get out of this... 😐