I realise I made the wrong call by posting this issue to that annoying place called Reddit 6 months ago, so I'm posting it again here where it belongs.
I've made this topic because I've discovered I have an issue which has terrible coverage online and no single hub of discussion. I only discovered its cause 7 months after I first had it, because it was notoriously difficult to reproduce.
According to my research, this issue affects AMD CPUs (at least Ryzen, FX and Phenom). Motherboard doesn't matter, Windows version doesn't matter, graphics card doesn't matter, RAM doesn't matter.
At random times, the monitor(s) will cut to a black screen (no signal), and fans will immediately speed up to default-default settings (pre-POST). Power continues to be supplied (including to peripherals), but nothing will work, not even the power button or reset switch, forcing you to switch off the PSU or mains power and switch it on again. For me, half the time, the PC would automatically reboot after the blackscreen, exactly mimicking the effect of the reset button (though I ruled out the reset button as a cause by unplugging it). I did not have any BSODs or minidumps. There was nothing about it in my Event Viewer either.
The frequency of the issue is very unpredictable, but it started immediately after I built my computer. It happened to me on the following dates (I kept a manual log):
31 August 2018 and 2, 10, 17, 18 September 2018
8, 9, 10 February 2019
8, 9, 10, 13, 14, 15 March 2019
HWiNFO logs leading up to the crashes in March showed nothing out of the ordinary, even in the last second before blackscreen. Stress testing in Prime95 and Superposition could not induce the issue. On one day in September, the computer even woke up from sleep straight into this black screen state.
I noticed during March that the problem was occurring when I had HWiNFO, MSI Afterburner and ASUS AI Suite open at the same time. I then managed to confirm online that the cause of the issue was some sort of conflict involving multiple hardware-monitoring softwares running. Sources specifically point to a CPU thermal sensor issue.
I was not monitoring the HWiNFO ASUS sensors which prompt a warning of instability in March. Also, the problem previously occurred when I had CPU-Z, CoreTemp or Speccy running instead of HWiNFO. The problem may also have happened when only AI Suite and Afterburner were running. Other users online report the issue with various other programs that monitor sensors.
The workaround will be obvious – to avoid using multiple programs that could monitor the CPU temp sensor. But I've seen no information about a fix or the issue being resolved by AMD themselves. There are hints in some of the topics below that BIOS or driver updates have reduced the symptoms, but the only surefire way I know of to avoid this issue is to avoid running multiple hardware-monitoring processes (in my case, more than 2, it seems).
External links to topics of this issue:
^ caused by ASUS Aura temperature-based colour mode in a possible conflict with other software
^ caused by ASUS Aura + ASUS AI Suite
^ caused by HWiNFO + CPU-Z + Afterburner, or HWiNFO + Corsair Link + Afterburner
^ caused by HWiNFO + Corsair iCUE (+ maybe another application)
^ caused by AMD Overdrive thermal sensing in a possible conflict with other software
^ caused by AMD Ryzen Master + ASUS AI Suite
^ cause unreported
^ cause unreported