@Chrome, With my electronics hat on, my guess would be a bad connection somewhere in the FQI system. Bad electrical connections can be very temperature sensitive* and this could easily have been a duff joint that went bad as it went through a particular temperature but recovered as the temperature changed.
Or it could have been that fuel contents were transferring. On Airbus I sometimes notice FQI errors while this happens but when the transfer stops the FQI reads correctly again. Having said that, the most I have seen on the A320 family is 400kg temporarily missing.
*Indeed, temperature changes are used to find duff joints when trouble shooting. We use freezer spray and heat guns to target suspect joints.