Google/Nest speakers won't connect

I am trying to connect a Google home mini speaker, and a Nest Audio smart speaker to my XB8 gateway.  Both devices get to the last step of the setup, and to paraphrase the error, the setup was successful, but the devices are unable to connect to the specified wifi.  The prescribed fix is to disable guest mode on the router and enable plug and play.  Plug and play is already enabled, and from everything I read, disabling guest mode equates to turning off the xfinitywifi ssid, which is enabled on my gateway.  However, the two published methods for disabling the public ssid (via the wifi advanced settings on the Xfinity app or through the account internet setting on the website) fail.  Both indicate that the page does not exist.

This is a two-part question:

1) Why will these speakers not connect to the XB8 gateway.  These were moved from a previous network that had an older Comcast gateway, where we had no problem connecting them.  And yes, I factory-reset both devices prior to setting them up.

2) Why can't I disable the xfinitywifi ssid using the two prescribed methods.  Why does it appear that these options have been removed from the app and website?  I also tried to find an option by logging onto the gateway directly, but can't find it.

Thanks in advance for any help.