@lduboeuf
When i first boot up, running top it tells me MiB Mem is 3593.7 total, 1521.1 free. Assuming MiB means mebibyte, that converts to 3.77 GB. And after accounting for memory allocation to hardware etc, this seems like it is all being recognized. (The Pixel 3a has 4 GB memory.)

Is there a way to test whether memory is faulty? I don't think the memory is bad, because as you say everything else is working fine, but i don't know what else to check. These blips seem to occur in groups. Last night's caused the reset, so i should have a "clean slate" upon reboot, but it happened again quickly after the reboot.

But it's been fine since that second reboot. I lasted the last two weeks nearly without a crash, and i've certainly been texting all that time. So... yeah i am baffled too.

-Fizz