[solbero]

I think you might have this bug, since you are sending the audio and video signals to different devices:

Audio devices are disappearing with pulseaudio 8.0 (Ubuntu 16.04) especially while running kodi and while using Adjust Refreshrate to match video. This is an issue with the module-switch-on-port-available module and will be fixed with pulseaudio 9.0, the fix sadly won't probably make it into Ubuntu 16.04. As a workaround please disable that feature by editing /etc/pulse/default.pa and commenting or removing load-module module-switch-on-port-available and reboot the system.

So, I would install PulseAudio again and try the fix mentioned above. See if that solves the problem.