Electronics can fail due to overheating, overvoltage, and mechanical stress. Are there other causes?
Yes, there are other mechanisms.  In fact, it's impossible to give a complete list.  This is softof the same problem as proving a negative.  The best anyone can do is list the mechanisms they know about.  Some additional ones are:

Chemical.  Dropping most electronic things into a vat of boiling acid is going to kill them, but chemical processes can be more subtle too.  Nothing is ever absolutely sealed.  Corrosive agents will diffuse thru any barrier given enough time.  Even just one assembly line worker with a little lunchtime salted peanuts residue on his hands can contaminate a whole batch of epoxy used to seal chips.  Those chips then have a high failure rate months to years later in warm and humid environments.  That's just one example, which actually happened.

Loss of essential substance.  This is not really a mechanical failure since in some cases it is know this will happen.  Electrolytic capacitors suffer from this, for example, even when everything works as designed.  Given long enough, the electrolyte will diffuse out.  Certain gas-filled components have the same problem, like neon bulbs.

Someting is consumed as part of normal operation.  Batteries are a obvious example.  Incandescent bulbs is another less obvious one.  The temperature necessary to cause the intended black body radiation will also cause fillament molecules to evaporate off its surface, eventually causing it to fail.  As another example, vacuum tube cathode coatings degrade over time with use.

Diffusion.  Even without essential stuff leaving or bad stuff getting in, the stuff inside can move around.  Short of freezing something to absolute 0, you can't keep molecules from moving around.  Most of the time, these molecules will move around so slowly that something else will go wrong long long before this causes problems.  For example, P and N type dopants in raw semiconductor are essential to how transistors work.  These were diffused into the silicon crystal at high temperatures over hours.  At ordinary temperatures, the diffusion rate is so small that other things will happen before most transistors die this way.  However, the rate is not 0, and as transistor sizes decrease, this will eventually become a limit on lifetime.

Migration.  Diffusion is one substance moving thru another, but migration is outright bulk movement of stuff.  This is already a issue as the nm scale of modern chips.  The interconnects don't stay where you put them due to applied voltage and current flowing thru them.  This is something that has to be considered for very fine scale structures.

You didn't specify lifetime, so very long term there are other effects, like radio-active decay.  Everything except iron will decay, eventually to iron.  Most of the elements we build things with have such long half-lives that this is irrelevant on a human scale.  Still, we have harnessed this effect deliberately.  There have been spacecraft powered from the heat of radioactive decay (of strontium 90 if I remember right).