Firmware update changed the order in which power is enabled to peripherals?

Maybe! I could certainly see something like the firmware switches on something way heavier that pulls down an already marginal supply.

Remember the very early Raspberry Pis that had the polyfuses that dropped a little too much voltage from the "5V" supply, so a combination of shitty phone charger, shitty charging cable, and everything just being a little too warm/cold/wrong kind of moonlight would just make them not boot at all?