Background:
There is a typical network topology：

Some users might notice that, once the internet service fails, they are no longer able to access the NAS server from the local network.

The cause of the issue:
When the main Deco failed to detect the internet service, both Ethernet ports on the main Deco would work as WAN ports.

Why do we use WAN/LAN auto-sensing on Deco?
For the Deco Mesh system, normally it would have more than 2 units and each unit has at least 2 Ethernet ports; It would be time-consuming and confusing to find out which port should be connected to the ISP modem. And supposing that the WAN port is fixed, once this port is broken, the whole Mesh kit would be useless.

So the feature request for fixing the WAN port has not been accepted yet.

Since the problem only appeared when the internet service went down, once the internet service recovered, there would be no such troubles. And currently, the workaround would be connecting the wired servers to the satellite Deco units, instead of the main one.