This may be the issue here. You still need to have wifi connection enabled for Miracast over ethernet as a backup source. Other requirements include having a system updated to 1703
TCP port 7250 should be open on router
Both devices should be on same network.
Quote : On Windows 10 PCs, the Projecting to this PC feature must be enabled in System Settings, and the device must have a Wi-Fi interface enabled in order to respond to discovery requests that only occur through the Wi-Fi adapter.