Overclocking/Undervolting is safe if you know what you're doing. If you don't know what you're doing then you end up with instability issues. You likely undervolted too far meaning you went below what the platform was comfortable with. Bump the undervolt a couple of notches to a prior setting(with a little more, not less, volts) and see if the issue persists.
Mind you, you're only advised to undervolt the CPU(core and cache) and the iGPU. If you're comfortable with what you currently have dialed in, you then go into discrete GPU undervolting. You will need to stress test your undervolting as always since there's no magic number you slap into a software.