the videos is not working for me here… so can only go by your description.
it could be that hermod is not calibrated to exactly zero volts, this is not that uncommon (my MI marbles also does this)
what I do is tune oscillators whilst I send C3 from hermod (you only only have to send it once, since stays at the same cv till the next note is sent)
you can also ‘fine tune’ a particular track, on effects -> midi ->fine tune.
I generally find eurorack voltages and therefore tunings are not very precise - and have found its best if you need very accurate tuning to tune, to a particular sequencer and output (aka track)
finally, if you think its bad enough, you can recalibrate hermod.
https://squarp.net/hermod/manual/settings - “How to calibrate the 8 CV outputs”
to do this you need either an accurate voltmeter,
or an oscillator (that you trusts its tuning!) that handles -4 to +4 .
id probably not calibrate, unless you have the tools, and the scaling was out (as opposed to a small offset in voltage)
note: the hermod has no feature (afaik) to recover the factory calibration… hence why I’m hesitant to advise recalibration.