I had the same problem with Samsung phone not being detected. The only way I've found to make screen mirroring work is to:
Settings >
System >
Advanced System Settings >
Network Connection Reset >
Reset Connection >
The TV will lose its WiFi Connection, but will now detect the Samsung Android Device
When you are finished, you will have re-enter the WIFI Password
The standby light will be blinking, indicating it has no network connection
Yes, very annoying...but works
Maybe they will figure this out