If there's only momentaty shock when touching, that could be ESD.
(colder winter weather is favorable for forming of static charges)
NUC doesn't use normal ATX PSU so at least it's not Y capacitors inside PSU.
Without safety ground those cause casing of PSU float half way between live and neutral, which causes constant "tingling" shock.
Though if badly done its power supply could have some AC leaking into its output ground.
Some badly done USB chargers for example have actually risky amount of AC in their output ground.