Having the same issue with Assault. Requires rank 11 to unlock the Piat (RPG) - I'm now rank 16 (in assault) (My rank in game overall isn't the issue) and it remains locked. This is a pretty game breaking issue as gadgets and weapons can't be accessed when they've been achieved in the HUD. My progression tree even has it checked. But if i go to the gadget menu, it has a lock and says available next round. Round after round it's said that.
Edit update
* After about 4 hours it updated. A number of melee weapons did too. Perhaps their stat engine was lagged, or the EOR trigger failed for some reason on the server I was playing on. In any case - my missing stuff showed up now.