Question WHEA_Uncorrectable_Error/No POST

[poodledook]

Hiya friends
So this has been killing me for a while:

Intel i5 9600kf
Deepcool Gammaxx 400
MSI Z390 A Pro
2x 8GB Crucial DDR4
Corsair 650W 80+ Bronze
Gigabyte RTX 3060
1x M2 SD 240GB WDigital Green
1x 1TB Samsung QVO SATA
1x 2 TB Samsung QVO SATA

I've been having this issue on and off over the past couple months. PC will run perfectly fine for long stretches, couple of weeks, no issues at all. And then at random it will blue screen with a WHEA_Uncorrectable_Error. When I get the system back working, I look at Event logs and it points at a CPU issue. However, sometimes it takes a long time to be able to boot again, as the PC will often refuse to POST for stretches. Debug light shows CPU issue. Not overclocking at all anywhere on the device.
This usually resolves eventually but it's really difficult to pinpoint the root cause of it. Sometimes repositioning the machine will do it. Sometimes it's reseating SSDs. Sometimes I reseat the cooler and heatsink. No rhyme or reason to what fixes, but it eventually comes back up and will either immediately go into another cycle of WHEA BSODs or run fine for weeks.
I've read through the stickied post around POST issues. I'm happy that;

• I've read the Mobo manual
• The CPU connector is plugged in correctly (and the plastic guard is off), fan plugged in
• Standoffs are good from what I can tell (though I've ordered a replacement cooler which will be arriving shortly just because this is what my gut is currently telling me the issue is)
• GPU is fully seated and powered
• Have tried with one stick of RAM, and I'm happy that it's in the right slots
• No bent pins or thermal paste spillage
• No loose screws or anything
• BIOS supports CPU
• Reset CMOS
• Connections are tight and good

I don't have integrated graphics, so not able to check that, and I'm not someone who has spare parts to speak of, unfortunately.

Something I've noticed is that it tends to get worse whenever I move the PC - it gets moved from downstairs to upstairs and back occasionally. Currently it's sat downstairs and has been for some time - able to launch Windows, but I'll get the BSOD WHEA error maybe once a day. Last time it failed to POST would've been maybe 4-5 days ago. That time it was fixed by gently tugging on the CPU cooler once.

I've previously been advised to run Intel Processor Diagnostic tool and I got these results

I suspect this will end up costing me some money - new CPU, or mobo, or PSU. But I'd like to narrow it down as much as possible before I commit to spending real money. If you can help me isolate the issue - fantastic. If you can help me fix it, I'll do all your chores for a year.

 

[poodledook]

Update: I put in the new cooler - now it just won't POST at all. I'm going to guess that that's a fresh issue, and I've done something wrong during the install.