@Ivan3z Any solution to this yet? Also could you please share the bug report
Edit (Solved)
You can either set allow background sound in the editor preferences
or
add the following to DefaultEngine.ini (project folder) or to your unreal installation BaseEngine.ini
[Audio]
UnfocusedVolumeMultiplier=1.0
This can also be added to any (other) Unreal-based game you have bought, if there’s no support for such through their options.
My case was very peculiar because I’m running two clients and I only need audio from one of them (one “game”, another is a control panel of sorts - connected by networking). To solve that additional problem, I added au.Debug.SoloAudio to commands.