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:
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.