My PC and a few other devices are connected to the Hard Wire Ethernet ports on my Deco system. 

When the Internet goes out they all get disconnected from each other and I can't use them until the Internet comes back online. 

The Wireless Devices stay connected, but not the Ethernet Cable Hard Wired ones.

Q: How to fix this?

Update:

A Customer Service Tech said Deco doesn't allow Hard Wired devices to be used without Internet Access while in Router Mode.

I asked "Why?" and was told, "That's the way it works by design"

Why on earth would it need to Disconnect only the Wired Network when there is no Internet?