We pretty much continuously produce weapons, so of course you're gonna find a few that are expiring right about now, because it's cheaper for the US Government to pass them off to be used than it is to dispose of them safely ourselves. There are ATACMS that expired a decade ago, and were disposed of without starting a new war.
In addition, the ATACMS program specifically ended in 2007, so under a Service Life Extension Program, the US Army has been pretty continuously refurbishing them to maintain inventory. All in all, this is a prime example of confirmation bias.
But also yes, defense contractors are the only ones who profit from war.
I suspect the failure rate goes up. Have you seen the video of the Russian AA missile pretending to be a boomerang 🪃 and flying back to its launch point?
Yup. One issue from long storage is that the fuel in solid fuel rockets can start to separate. Ryan McBeth did an explanation on a possible cause on that AA missile failure.
As you mentioned, some explosives also become unpredictable. The Takata airbags sending shrapnel into drivers faces comes to mind.
Yes, I've seen (that?) such a video. Rockets and missiles have a lot of mechanical and electronical parts that can refuse to work properly when overaged or stored under bad conditions, besides fancy things happening to the explosives.