with bolded, i think there may be issue with specific hardware and best if you can run stress test/memory test etc to rule out what specifically is causing the issue. (maybe psu voltage instability? memory sticks? maybe swapping the stocks around? possible to swap hardware such as cpu/mobo/memory etc?)

increasing voltage while keeping stock clock MAY help, however it is a workaround method dodging the original issue and you gain nothing out of it as increasing voltage also potentially reduces component lifespan/increasing temperatures while not gaining performance which seems very detrimental and totally against the original intention to increase voltages.