[PROBLEM] HDMI is problematic...

[Evotz]

This may or may not be relevant..
I have an HDMI monitor that failed the edid most times (like your 'works occasionally') and I tried all the recommended RPI settings for HDMI without success.
Then discovered that the monitor (substitute your AVR) had an extremely fast time-out on start-up...
If I started the monitor before the Pi and was too slow starting the Pi then the monitor timed out and the Pi could not find it...
If I started the Pi first then by the time the monitor booted the Pi had found no suitable device and that was that...

Finally, having twigged to the timing, I was able to start both and have the Pi detect the monitor correctly.... Once I found the sequence I am able to boot both consistently..

No idea (blind venison ?) if this is your problem but in the absence of other fixes I thought to post my experience...as usual...ymmv and i may be way off beam...
Cheers,
Bob

I admit, I'm relatively new to moOde, and I ran into the same problem as you with the HDMI/monitor power-up timing issue.  I searched this support forum and it seems like people who are using the HDMI for output are in the minority, so discussions related to HDMI was very few and uneventful.  I have a Pi 3B+ configured to only use HDMI audio.  I only turn on the monitor to do maintenance (i.e. updates etc) or when I want to search my collection on a bigger display (I am presbyopic).

Nevertheless, for my setup, to get the audio and video output from the HDMI working flawlessly without conforming to the critical timing or performing any rituals, I have these lines in my config.txt

hdmi_force_hotplug=1
hdmi_force_edid_audio=1
hdmi_drive=2
hdmi_group=1
hdmi_mode=16
hdmi_blanking=1

And for good measure, I have also disabled HDMI display off timer within moOde configuration.  Maybe if there's enough requests for these additional HDMI "features" (and do ask nicely), Tim can implement these hard-coding options within moOde configuration. 

Hopefully the information above contributed to our community.

Best,

EVO