Hello JI_BO_CHANG1013,
This is a common issue in Battlefield V, but it can be easily fixed by talking to EA support. They are able to award you the missing assignment.
I have the same problem, I wrote to support and they said the problem is unsolvable.
They should still be able to do it as far as I'm aware, but I guess they might have lost the tools now since it's an older game. However, if it was me, I'd give them another try in case the first agent was incorrect or just didn't know the solution.
I contacted support many times and the answer was always the same: they can’t solve this problem because support can’t make changes to the game.
I can confirm that they are still able to give you the missing assignments, just make sure you explain your situation in detail. Thousands of players go through the same process and are successful with it III_SAINT_III.
