I’m not sure that I would call it a power failure right from the start, but you are correct: It looks like the RPi is spontaneously crashing - for whatever reason.
You could use the information from Raspberry pi crashing during "make" command - #17 by Sineos for example to stress-test your unit, and maybe you can watch it crashing live and in color.
Generally @EddyMI3D is right: Power supplies are good usual suspects on RPis but I have yet to see that
solved anything. For me, this is a bit of a myth and the actual root causes were something different.