I'm getting random reboots, tied to nothing. Micro computer, AMD Ryzen 5 5800H. New (<6mo) computer; no re-used old components. 36GB RAM, which has passed a few runs of memtest. I have regularly seen the k10 temp spike to the low 90s without reboot, and when the reboots happen I haven't noticed that the temps were higher than 60. The only thing I've been able to correlate it at all to is composing email; I'm a fairly fast typer and markdown-oxide goes berserk and consumes in the mid-high 100% CPU use (~165%) while I'm typing. I made the correlation because multiple times this has happened has been while I was composing emails (and subsequently lost them).
There is nothing in boot-1 logs. Just normal logging and then reboot. Nothing at all suspicious, no weird errors. I struggle to use more than 50% memory, so memory contention is not an issue. It's like a sudden power cycle.
The system is on a UPS; my next avenue of investigation is the UPS itself, but power surges in the house shouldn't be a possibility; there are a half dozen other computers in the house, some on UPS, some not, and none of those are having issues.
I saw an article a few days ago about a tool to help track down mysterious reboots like this, but can't find it now. I don't know how software could help; it is literally: everything is working, the screens go blank, and in a second or so the BIOS posts.
I am suspicious of the CPU core temp readings, which I can't seem to get at. I get the GPU temp, which is never stressed (stays around 45C); and k10temp_tctl, which from what I can find is an edge temp and not the core temp; and all of the NVMe temps, which all stay in the 40s. But the fact that I don't know if I'm seeing what's really going on temp-wise in the CPU worries me. But I don't think I've had it crash during a software update, which often includes compiling a bunch of Rust, C, Go, and whatever packages which I can see pegging multiple cores.
I'm at a loss. I've looked at everything I can think of, but still haven't gotten a hint about what is triggering this. I may just do a bunch of markdown editing with markdown-oxide enabled and see of I can reliably force it to happen, but that still wouldn't tell me why. I am certain it's not memory, and have mostly convinced myself it isn't temperature, unless it's something hidden I can't get a reading on.
Help?