BF1 assignment / weapon unlocked but after restarting the game its gone

Hi all,

Something weird happend. Last week i joined randomly an overseas server, had a high ping around 110 but i played conquest on the map Achi Baba. I used the infiltrator kit and got a lot of kills with it. The weapon ''Ottoman Kilij'' was unlocked during that game and had used it couple of times. Also the next games i played with it. 

Till after i quit the game and wanted to play it again in the evening. I saw that the weapon was locked again and had to complete the assignment while earlier that day i already completed it. 

Now after a week its still locked.

Any ideas?