I no longer have my R3,R5, or soundbar connected to smartthings (and don’t plan to readd them till ST properly implements them and they are stable). But if memory serves me right, the connection to ST is based on IP. If you are connecting your speaker via 2 interfaces (wireless and wired), each interface will have a different IP but ST will only be connected on one of them. Your Samsung multiroom app will always find it because it scans the network every time to display your connected speakers.
So here’s my recommendation.
- remove your speaker from ST altogether including the smartapp.
- remove the lan cable and ensure your speaker is connecting on the wireless network.
- setup a IP reservation on your router for your speaker on the wireless connection and document this IP.
- readd the Samsung connect smart app to ST and hopefully it will find your speaker on the wifi.
A great mobile app for viewing, documenting and troubleshooting network connectivity issues like this would be the Fing app.