Last week, the HDMI blacks out intermittently. And last night, suddenly went to protection mode. Was not even playing it loud. Power off and on. Then seems to be working.
Wonder if this is sign that bigger problems will happen soon. Less than 8 mths old. 
Which HDMI cable u r using ?
Do you have proper ventilation?
The HDMI cable are non-branded stuff. But I don’t think that’s the problem. I’ll try to swap to a different cable to test.
The AVR is now totally well ventilated. No cabinet around it. But I did not add an extra fan for it.
I’ll run more tests tonight… It’s better to know for sure if it’s a problem or not - especially when it’s still under warranty.
If it’s blackout intermittent issue, very high probability it is the hdmi cable . Swap in the Moshou cable the problem should go away.
Try and maintain 2m hdmi cable length whenever possible, that’s your magic number . This works very well
I can loan you if u want, I have a spare I use it for music tidal
If it solves your problem, you can buy one from aliexpress. Oh ya, it’s 11.11 ! Should have some discounts !
I think you are more concerned about the sudden shutdown issue. 
Don’t tell me the hdmi cable u r using is a monoprice. The last I recalled, all 3 of us, myself, my uncle and his friend, all have to send in the Denon to replace the hdmi board
Oh I read that somewhere before. Hope not the case.
Crossed speaker cables? Using banana connectors?
I have the Amazon Basics hdmi cable. Really? Can mess up the denon hdmi board? Why would that happen?
One observation is that the blackout happened when the source was from my PC (running a Wavlink Display link multi port). Running from nvidia shield seems very stable, no blackouts at all (yet). Maybe problem is from PC.
But what puzzled me more was the receiver going into Protection mode. Was not even playing loud nor for very long period.
Pretty sure no crossed cables. Banana plugs front speakers. Bare wire at surround speakers.
You mean u are able to replicate it more than once to get the AVR into protection mode?
Protection mode happened only once. But I’m puzzled why it happened in the first place.
Check grounding, especially if your PC and AVR are powered by wall plugs far apart.
With one end of the HDMI cable connected to AVR or PC, at the other end of the cable if HDMI connector shield give you a very slight tingling sensation when touched, you have a grounding issue.
Several years ago, I had grounding issue that caused AVR to go haywire and occasionally shutdown. It was traced to the TV, and then finally to the Starhub CATV grounding. With the CATV antenna disconnected, no more issues. This may or may not be the same as your case.
I think no issue lar. This is probably a one-off incident. Unless it happened more than once, else I wouldn’t lose too much sleep over it.
Googling a bit more… some say hot-swapping HDMI cables is a no-no… OK, I’ll try not to hot swap anymore… lol… I’ve done it quite a few times.
My PC is using a Wavlink DisplayLink USB C HDMI and DP docking station. Using Display Port (DP) to my work monitor and HDMI to AVR. So, the blackout happened when was watching stream football last Saturday. But yesterday, I ran youtube for over an hour without any blackouts.
Anyway, I’ll continue using as normal. Hopefully, problems won’t happen again. If it does, maybe I’ll send the Denon to service center (hopefully before end of warranty)
That’s a big no-no. Worse case scenario is short circuit the whole HDMI board and that’s it.
Our case was with the redmere hdmi from monoprice. Very scared of that brand
No no for hot-swapping HDMI cables. Always turn off all the equipment before swapping.
Likely that is the case . I will always tell my client not to treat it old school method plug in and out like composite or component connection cables .
In the old 1080 p the passive and active cables will also cause issues which leads to burning the hdmi board .
Now it will be more sensitive as most 4k are active cables .
Just note to self switch of all incoming source before connecting . Or best switch of every thing and connect every thing . That will allow all equipment to have hand shake connection .
Hope nothing wrong with your equipment .
As long as there is still image and sound…it should be fine imo.