Most likely bad capacitors. The https://en.wikipedia.org/wiki/Capacitor_plague may have passed, but electrolytic capacitors are still the major life-limiting component in electronics.
They still degrade with time, but in a very predictable way.
That makes it possible to build a version of your design with all capacitors '50 year aged' and check it still works.
Sadly no engineering firm I know does this, despite it being very cheap and easy to do.
https://www.badcaps.net/forum/troubleshooting-hardware-devic...
Most likely bad capacitors. The https://en.wikipedia.org/wiki/Capacitor_plague may have passed, but electrolytic capacitors are still the major life-limiting component in electronics.