alt Hacker NewsBank of France "transported" their reserve by selling the gold held in New York, and subsequently buying the same amount in European market.
They opted to do so because it's just more efficient. It takes a lot of efforts to physically move 129 tonnes of gold after all. And as a side effect of this relocation project, they ended up recording a capital gain. It's nothing-burger.
The transport would likely be quite expensive as well. Lots of armed people needed to move gold around, plus special vehicles.