Country

Germany 

Device

iPhone 6 (iOS 12 beta 5-8), iPhone 5S (iOS 11.4), Apple TV 4K (tvOS 11.4)

My Question or Issue

I guess since tvOS 11.4 or iOS 11.4 (Airplay 2) I'm getting Mono-Audio when I stream audio from my iOS devices. 

I noticed it because just my center-speaker on my 5.1-system plays audio (using Dolby Pro Logic II). 

When I switch to Apple Music, all speakers are active.

My current workaround is:

1. Start Airplay connection from iOS control center
2. Start song with Spotify (getting mono audio)
3. Switch to Apple Music, start playing a song with Airplay still active (getting stereo)
4. Kill the Spotify app from the multitasking switcher and start it again
5. Spotify plays now in stereo, all speakers are active.

I can always reproduce this issue, but I couldn't find any other thread online. 

I also filed a bug report to Apple.

Can anyone with a similar setup confirm this issue?

Update: I could localize the error better. See my answer below. A better workaround now is to kill the app via App switcher (swipe up). Then connect to Apple TV via control center and start spotify again.