@AnotherName

How exactly are you testing? 

When I enable "Guest" and connect my Cell to "Guest", I can no longer launch the Deco App, I can no longer reach any of my streaming video hardware.

And while performing a network scan from my phone, there are no devices active except the router on port 443 and my cell.

The only thing I can do from the cell when on "Guest" is access the internet. 

I have an extended Deco M5 MESH. 

@AnotherName 

I had my laptop on guess and everything else on master. I ran a network scan using avast free antivirus software on the laptop. It was able to locate the other 19 devices on master network including the device type MAC,ip address and all port being used. 

@AnotherName 

Were you connected to Wi-Fi or via Ethernet?