Updated to Mesh Wifi and thermostat won't connect to app

[Zamfir]

We recently replaced our router with a Nest Pro Mesh Router system.  The thermostat is online but will not connect to the app.  I reset the modem.  I reset the thermostat.  I reinstalled the app.  Nothing has worked.  So frustrating!

[Patrick_Caezza]

@Zamfir 

Do you still have the ISP modem/router installed?

Is its Wi-Fi still turned on?

Did you use the same name and password on the mesh system for the Wifi?

[Zamfir]

Thanks, @Patrick_Caezza. We have the ISP modem but took back the router when we got the Mesh. 
We have WiFi. 
We used a different name for the mesh but the same password. 

[Zamfir]

When we reached out to the ISP, the rep said she did not detect a router, but I had run out of time to proceed further.  Is this common?