In fact, there are reasons for the differences between Loadsheet CG and ECAM CG.
Loadsheet assumes an ideal fuel distribution for a given FOB, but real fuel distribution may not be so. For A 330, if somehow -even small- amount of fuel left at Trim Tank (e.g due to some maintenance check) and the FOB is less than 36500 Kg, then ECAM CG may be quite further aft of the LS CG.
Apart from this, real Fuel density may also effect this difference particularly when all tanks are full. This is because, LS is also prepared by assumed fuel density unless it is specifically given for that fuel loading. Even small differences between LS assumed Fuel density and real measured density by tank densimeters, may cause big difference between two CGs when the amount of FOB is near max.
The reason for 2% is another story. The LS CG limits are operational limits and these limits are, in general, around 2% shrinked (narrower) than the Certified envelope (as published in FCOM). When ECAM CG is diffrent than LS CG, practically there is no way to ensure this CG is still within Certified CG envelope, unless this difference is less than 2%
