Brand new Arris SBG10 Gateway cannot connect to Comcast Internet

I'm trying to replace my Arris SBG6580 Gateway with a new Arris SBG10.   I have called Comcast customer support and used the Xfinity app to register the new gateway.  I have correctly added the MAC Address for the new gateway.  After 11 minutes the app times out and will not accept the new gateway.  I don't remember the message but it just states not found or something like that.  I have tried this a number of times. 

I then use the Xfinity app to reinstall my old SBG6580 gateway and that works fine without any issues.   I am pretty confident that there is nothing wrong with the new SBG10 and my internet works fine with my old gateway. 

It appears to me that somehow Comcast is not accepting the MAC address of the new Arris SBG10 gateway.  I have  tried the app several times in my home and also at a friends home with the same poor results.  Is the MAC address of the new gateway not being accepted by Comcast for some reason? Please help.