Display driver amdkmdag stopped responding and has successfully recovered.

This sounds exactly like my issue, I was thinking it was only related to my vr headset, but I really only play iRacing and Assetto Corsa, with some occasional COD and mine has similarly never had this issue with COD.
The ~20-30 minutes after cold boot is spot on though, and I've run hours long races on iracing with massive fields of cars after the first crash of the day with 0 further issues.

Going to try to replicate this and see what I come up with.

Which motherboard/RAM combo do you have? 

My system:
5800x (also had this issue with a 3700x within the past month, on both most recent bios and the version that shipped with my mobo)
asrock taichi 5700xt
msi x470 gaming plus max (latest bios)
corsair vengence 3600 C18 8x2

Edit: swapped ram to only run single channel in dimm a, seems to have done the trick first time. I'll update this post if that I end up getting a crash, but I jumped in an iRacing lobby very quickly after a cold boot, which is usually a surefire way to get the crash quickly and it never came after almost an hour and a half.

I do think this is related to the AMD HD audio device driver solution that's been posted in this thread as well however. I've only seen these crashes in vr, which is the only time I use AMD HD audio, because the vive cosmos can either use that for sound through it's hdmi plug, or through usb using standard audio. I've also noticed after these crashes I often have issue with the audio device to my vive cosmos. But this has never once happened when using a corsair usb headset which has its own drivers.

I'm going to give it a few more days to shake out and see if this resolved it, but as of right now I'm thinking this is an issue the with AMD HIGH DEFINITION AUDIO DEVICE causing the whole gpu driver to crash, probably related to memory timing or something based on running single channel ram not causing this issue (again, if this is truly fixed).

Pasting some terms from my error logs for SEO so hopefully I help someone else:
Display driver amdkmdag stopped responding and has successfully recovered.
The application-specific permission settings do not grant Local Activation permission for the COM Server application with CLSID

Bizarre. I think I tried the audio solution in the past with no luck. We have the same motherboard and similar memory...

My parts list:

MSI X470 Gaming Plus Max

Ryzen 3600

MSI 5600XT Gaming X with updated 1750Mhz memory VBIOS 

Corsair Vengeance 3466Mhz C16 (CMK16GX4M2Z3466C16 ver 4.31)

RAM is running at the stock 2666Mhz now, no XMP overclock and I got a crash in dual channel mode this AM in PUBG. This is with the latest BIOS so it's not fixed by BIOS updates. 

I get the same "amdkmdag stopped" error. Also if you open reliability monitor do you have red "X" symbols and Windows "Kernel Error" events that correspond to the crashes?

Will double check for the Kernal Errors later, but I think I have seen them. 

What audio device are you using when you play? Do you use something that says AMD HD AUDIO DEVICE after it? I'm still heavily leaning towards that being the culprit.

I use either of the "Speakers" entries from the screenshot. By this I mean the "Speakers (Logitech PRO X Gaming Headset)" or "Speakers (High Definition Audio Device)"

I never use the AMD High Definition Audio Device.

Also, another update related to the memory; when I run in dual channel using DIMM A1 and DIMM B1 the crash occurs too. So in summary so far:

1. Dual Channel (2 x 8GB) using A2 and B2 (Recommended slots per the manual) = Crash
2. Dual Channel (2 x 8GB) using A1 and B1 = Crash
3. Single Channel (1 x 8GB) A2 = OK
4. Single Channel (1 x 8GB) B2 = OK
5. Single Channel (2 x 8GB) A1 and A2 = OK

I'll try to complete the list in a future post.