Help, please! GPU hardware or driver issue in 2019 5k iMac? Plus new Big Sur Photos issue…

[wills11]

I bought a new iMac in November, 2019. It would sometimes have a kernel panic when restarting. That went away for some time, but now it's back, intermittently—and I'm unable to find a way to reliably reproduce it. It only seems to happen when restarting, and from what I can tell, only when I'm using an external monitor (USB-C to HDMI adapter in TB3 port), although I almost always use two monitors. Current panic attached as text, and it starts with:

panic(cpu 4 caller 0xffffff7fb25b115b): "virtual bool IOAccelLegacyDisplayMachine::display_mode_did_change(uint32_t): AMDRadeonAccelerator driver returns false"@/AppleInternal/BuildRoot/Library/Caches/com.apple.xbs/Sources/IOAcceleratorFamily_kexts/IOAcceleratorFamily-439.35.4/Kext2/IOAccelLegacyDisplayMachine.cpp:267

Anyone have any suggestions? If it's hardware, I'd like to deal with it in the next two weeks before the 1-year warranty is up. I've read many threads about it, mostly on Apple forums, but most people seemed to experience it with MacBooks (and often external monitors). I tried various suggestions—some were to do with Energy Saver preferences—but have had no luck.

And… after upgrading to Big Sur, I noticed glitches Editing in Photos—specifically while adjusting contrast and other settings. This happens regardless of whether the Photos app is on my iMac screen or the external monitor. Attaching video and still photo—and would so appreciate any input, or even just to know if others are experiencing this issue.

Thanks so much!

William

 

[LadyNinja]

I have also posted a thread about it. Not much respons... It happened in bridge and photoshop. Not lightroom. This is on the new 2020. Had it in for a fan fix. They sayd its probably software and i could test it with other programs.
I read that ps is more GPU hungry. So that made be sceptical with all the previouse fuz about it.
Like Jesus, my 2012 runs ps fine....

It suddenly runs a little better in photoshop. But more of the sdjustment needs to be made in 64% view. Any larger it either starts to pixelate the sdjustment or very laggy.
Just very tired off the problem and this computer. Have only found a work a round. Adobe is well known for its problems as well.

 

[sbw113]

On my iMac 5K I've been having startup issues when restarting/booting. It happens a lot. It was happening on Catlina, and continues on Big Sur. I've done a hard drive wipe (remove all partitions and start fresh) installed via Internet boot and installed new OS. Still happens. I've run hardware diagnostics at boot and it comes back clear. I can always boot into safe mode with out panic happening. Oddly, it seems if I have no USB devices connected the restart panics are less common. I haven't had display artifact issues.