Certain apps and websites on devices won't load/open while connected to XB8 router

Hello! We got a XB8 gateway yesterday. Everything connected and worked at first through WiFi on the router. Now, the ecobee thermostat, Alexa Echo, and certain apps and websites on Android and iPhone won't connect.

For instance, the Prime Video app won't open and load on Android. It works on mobile data, but not on Xfinity Wifi.

Please help me with a fix ASAP. Thank you.