Entry in the journal of the delivery changes on its own

screen-3.pngGood morning,

my stock must always be equal to 0 so always the quantity received must always be equal to the quantity delivered and the amount of the receipt is the same of the delivery, so far I have no problem, but in a while the amount of the journal entry of the delivery is different from the total document of the delivery.

Any ideas on where this change came from?