Most devices never test their memory and don’t have ecc, so you generally never know. Random instability can be fixed by restarting and your program not being in an area with bad bits anymore.

Anecdotally, RAM failures are more common than they used to be in previous decades, I assume due to increased capacities and smaller process nodes. Looser manufacturing standards may also play a part.

The component category I've never seen fail is CPU.

Well, you’re lucky. I had to change laptop memory sticks a few times. Though not since they are soldered directly to the motherboard

I recently had part of a 32 gig DIMM go bad on a 128 gig system. One of the larger VMs was spontaneously rebooting for no apparent reason. I was able to find the addresses with MemTest86 and map out 512 megs of the affected DIMM with the Linux kernel memmap option.

Same, it's either bad to begin with or it's basically immortal.

I've seen some fail. Might have had to do with the fact that the computers were literally flooded (river came up faster than the sandbaggers could keep up) while running.

This isn’t true anymore beginning with DDR4 speeds.

I've had a few RAM sticks fail, but the ECC usually caught it first. Also had one case that somehow the stick slightly unseated itself; dunno how but it was out of service for months until someone opened it up and reseated the stick.

...granted though I've also seen a backpane on a server fail. I didn't think that was even possible until that point.