They sort of hotfixed it; should hopefully fix itself when you complete one more game and visit the armory (you can't leave early).
DICE TeamHey @fatgorilla4,
Once the server you were playing on finishes and heads to EoR, the weapon should unlock. If you join another map before EoR on another server, you may have to play until the NEXT rank to unlock the item. So for example, if you unlock the MP40 at rank 4, you would have to play to rank 5, then the backend system updates you unlock.
/Atic
I also have this problem, says available next round - but have played many games since and still not available
