B450M Pro4 Overheating

Hey all, I've been having an issue for the last 2.5 years and I think I've finally diagnosed it to the Mobo. At 70C on the CPUTIN, I get a forced shut down (and cannot turn on for the next 5-10 mins). It's an odd issue, given that the max temp on the CPU reads at 115C in the BIOS and the CPU (a Ryzen 2600) is rated for way above 70. The CPU reports temps as high as 85 and it's fine, it's specifically when the motherboard's readout (I assume a monitor in the socket) reaches 70C that it shuts down. No idea why it does this, I've fiddled with everything imaginable and have updated to the most recent BIOS that still is approved for my CPU (3.5). I've replaced literally every part of this comp besides the MoBo, the processor and the case, but here are the current specs.

CPU: Ryzen 2600
GPU: 6600XT
RAM: 16 GB Vulcan-T
PSU: Enermax 650W
MoBo: ASRock B450M Pro4

I would just RMA the stupid thing, but because the issue was so impossible to figure out, the board is out of warranty now and ASRock says they won't replace it without a fee.

Others have reported similar issues as far as I can tell:
https://linustechtips.com/topic/1138618-pc-shuts-down-when-cpu-is-under-load/
https://www.reddit.com/r/ASRock/comments/oprp4j/asrock_b450_pro4_with_ryzen_3300x_overheating/

Different MoBo, same issue: https://forum.asrock.com/forum_posts.asp?TID=6144&title=mobo-shuts-off-when-cpu70-deg-f

If anyone can help it'd be wonderful, I've already dropped 800 dollars on various part upgrades to fix this and I'm going to be pretty angry if I have to shell out another 150 to replace this MoBo.