[MicTie]

Thanks!

But, I don't think my TV turns off, at least I don't see it ... I am sitting in front seeing some KODI animation while playing some music, and suddenly the screens turns black, next moment I see a screen generated by my AVR

It seems ALSA rescans after 10 minutes

UPDATE 1:
I did some further testing based on your comment, here is my findings
1) if the problem occurs, KODI does not switch off completely, only sound (via AVR) and picture (via AVR and TV) stops
2) if I play some music with TV off, after 10 minutes the sound stops
3) if I play some music with TV off, and also switch my AVR OFF and back ON, music continues playing
4) the 10 minutes seems to be from the 'power-on' of KODI, and not from the 'Power-on' of the AVR
5) if I play a movie for 15 minutes, no problem, if I continue to play music afterwards it switches off after 10 minutes

to me it seems that KODI is checking every 10 minutes and suddenly unable to find any output device,and stops playing - although this seems not showing up in the logs

UPDATE 2:
to pinpoint the culprit (cable, AVR, TV, KODI) I did some further testing:
1) change of HDMI-cable: problem occurs
2) play music via AVR with TV off and disconnected (eliminating TV): problem occurs
3) use different HDMI-ports on AVR: problem occurs
4) use different HDMI-input-device (Media-Player in Standby mode) with AVR: problem does not occur
5) connect KODI HDMI-out directly to TV (eliminating AVR): problem occurs

=> based on 2) and 5) I conclude the issue is with KODI

UPDATE 3 - SOLUTION:
(maybe helpful for someone who runs into the same issue)

add the following lines to /etc/X11/xorg.conf:

Section "ServerFlags"
Option "BlankTime" "0"
Option "StandbyTime" "0"
Option "SuspendTime" "0"
Option "OffTime" "0"
EndSection