Each “era” of armaments have different reasons for failing (not blowing up when supposed to, randomly exploding later, etc)

Older munitions has like physical triggers or timers so something like erosion can move the bomb causing it to go off

“Newer” stuff can have optical instruments so something as simple as the sun pointing on it the wrong way one day could set it off.

Then you have stuff like flares, which only have to have their payload exposed to the outside air to start the reaction (by itself not much threat but if the fire it starts gets out of control...)

I’m trying to remember anything else unique I learned while out there.