Basically there's two issues affecting electronic chipsets at high altitude : air density and cosmic rays.
The reduction of the air density can mess with the cooling system.
Cosmic rays contain radioactive particles which can cause soft failures to occur in solid state electronics.
EDIT : Found an interesting paper about it with more details : https://pdfs.semanticscholar.org/6046/529f05a65e182ac9323ef8...
Lower air density -> less heat transfer, so components run hotter.
Air pressure may affect disk drives and other sealed / fluid-dynamic systems.
Capacitors and other electronics might possibly be affected.
Apparently displays and printers (liquid ink) are strongly affected.
Arcing increases with elevation.
https://highaltitudelife.com/electronics.htm
https://www.eng-tips.com/viewthread.cfm?qid=24254
https://en.wikipedia.org/wiki/Derating
