BS, not that I'm doubting your actions, however one solution is that you turned the prime pumps on and not the transfer pumps off!
When I did the check, after turning the transfer pumps off, the main tank contents remained at a figure over 200 kgs, which I assume is as it should be.
Did you get any feedback from Airbus/Bond after the paperwork was sent in, or have you questioned it outside of an internet forum, as this episode seems rather strange.
Where did the fuel go, I have no idea.
The collective opinion amongst my colleagues is it's syphoning.
Is there a collective opinion about where the fuel syphoned out to?
It looks to me like the XFER pumps are delivering the fuel to the bottom of the supply tanks...
Therefore it can't be syphoning can it!