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Could be a faulty Y capacitor in the VFD. Maybe its gone a little short, though they should fail open...but thats assuming the makers used a "proper" y capacitor, and not some cheap alternative.

Of course, maybe they used a too big value Y capacitor.

Maybe they didnt use a common mode choke, or not enough common mode choking inductance....that would pertain to high frequency currents flowing to earth though.

Maybe some or many  of the installations where you work have other devices where they actually have too much y capacitance inside them...and your VFD is then adding to that and tripping out.......so that wouldnt necessarily be a problem with your vfd...but a problem with other peoples kit.

I lived in a flat block where the rcd kept tripping, and an electrician had to go through everybodys room to see who had the dodgy thing with too much y capacitance (or an insulation fault to earth) that was causing the overall earth current to be high anyway, and then often  it tripped because it was so near the tripping threshold........

Also, could be the insulation from one of the power semiconductors has overheated or something and so is breaching its insulation to its earthed heatsink.

Something in that VFD is connecting,  either directly , or capacitively, to the earth somehow.

But also, as discussed, insulation faults to earth are commonplace...so it might not actually be your VFD thats at fault....maybe the earth current in many installations is already well high, and then when you plug your thing in it just goes over that threshold....and trips the rcd.

Also, some places use cheap RCDs which trip at very low earth current....hooky RCDs from some cheap supplier.

Its no surprise you get dodgy RCDs because they are so expensive (at least the proper standards regulated ones are)...so some places skip out and use cheap ones that are trash.