But it also was never confirmed and thats a very rare cause where the RAM was running on too high voltage and the CPU on too low Voltage.
Actually this would be the fault of the overvolted RAM and not the undervolted CPU because the CPU gets constructed for specific voltgaes too hold and that must always be the maximum specified volages. because on peak when switching you can always have a minimum time when it goes up from minimum to full in an instant.
So in that case the hardware was already running out of specification and the undervoltig just gave it the rest (eveb though it's not is's fault).
So you are right in a way, that if you are using Undervolting you could rip open already existing hardware problems and thus sophistically kill your hardware.
But that won't ever happen to you because: Todays CPUs already use undervolting. they won't permit voltage changing under specified levels without really deep hacking. Using PHC on CPUs which don't meet those prerequisites makes no sense since they have no dynamic voltage scaling which is nonsense from every single aspect.
And the thing that at too low voltages the CPU might put out wrong results true is your own risk. But it won't kill your hardware.