A cosmic ray can flip a bit

Neutrons from cosmic-ray showers, and alpha particles from the materials of the chip itself, flip bits in memory. At the scale of a fleet, this is a design constraint, not a curiosity.

A high-energy particle knocks a charge loose in the silicon. If the charge is enough, a stored one becomes a zero, or the reverse. The effect was pinned down in the late 1970s, first from radioactive contamination in the packaging, then from neutrons born when cosmic rays hit the atmosphere. The rate in one chip is small. The rate in a million chips is a stream of silent edits. Error-correcting codes on server memory exist largely because of this, and because of ordinary electrical noise. They store extra bits so a flipped one can be found and put back.

A phone has no such code on most of its memory, and mostly gets away with it, because mostly is enough for a pocket. A bank, an aircraft, and a spacecraft do not accept mostly. Their machines assume the sky is a writer and budget for it.