My Setup I have a Denon AVR 1200W which is officially Spotify Connect certified.
It is recognized in the Windows, MacOS and Android 6.0 Client just as usual and i can turn it on as usual.
My Question or Issue I can't see my device in the Spotify App on my smartphone (LG G6 mentioned above). Even if the receiver is turned on it is not listed in the Spotify Connect list.
The only time i can see it in the app is when i start a song from my Windows, MacOS or Android 6.0 client to play on the receiver.
Immediatly after the song starts on the receiver i can see it in the app on my LG G6.
What i have checked:
My receiver has a fixed IP. I can even show the web interface of the receiver when i enter die IP Adress in the browser. So there shouldn't be a network issue.
I have UPnP enabled on my router so there shouldn't be any port issues. (as described above, starting a song from my Windows, MacOS or Android 6.0 client is no problem over the network)
Updated the firmware of my receiver to the newest version. Didn't solve the problem.
I have an older android phone with Android 6.0 on it. After installing the app with the same version number i can see the receiver in the Spotify Connect list. So the app has no problems on Android 6.0.
I recently updated my LG G6 to Android 8.0 (had Android 7.0 before). The problem persisted on the old and new Android version.
When i start the Windows, MacOS or Android 6.0 Client it immidiatly shows up on my LG G6 as available Spotify Connect Device.
Got any clues? I dont have any more....
The only thing i can offer you is some "deeper" diagnostics because my LG G6 is rooted and i can get some netstat commands running 😄
But i dont know on which ports the Spotify Connect Devices work or operate.