This article explains what happens when a LAN cable is connecting while using EloView 3 Configuration File feature

The EloView Network Configuration File only applies to Wi-Fi connections. However, if a LAN network is detected, the LAN will be used automatically by default. 

Also, if the device is connected via Wi-Fi and you plug in a LAN connection, the device will start using the LAN connection.  The existing websocket connection between device and cloud is not disrupted unless you lose the Wi-Fi or reboot the device.