Same issue here. Currently in the process of talking to EA support about it, given the advice when Tides of War has gone wrong in the past.
Looks like the reproduction for this issue is:
1. Be between 6 and 19 kills for the final Tides of War mission before the update
2. Login after update changed criteria to 5
3. UI displays Stug IV as awarded, but vehicle is unavailable for equip and is not present in shipments.
PC, was at approximately 14 kills last night. Have tried completing a match and restarting client to see if the item awards, but neither worked.
EDIT: Reply from support below in italics.
Support: Thank you for patiently waiting, I've checked our system in regards to any updates and found out that our Studio team have been informed of the issue and are currently investigating to determine the cause, as well as fixing it, but as a workaround that you can try is to do one additional kill to see if it will unlock the rewards for you.
Me: It's a pretty difficult one to get the specific kills. I'll give it a go, but I'm assuming that even if I don't get the kill I'm guaranteed the reward as it shows that I completed it?
(i.e. guaranteed the reward once they fix it that is)
Support: Definitely, all of the players who are eligible for the reward will get it once the issue is fix
If I am able to get another one of the specific kill types in question and it does pop the reward I'll come back and upade this post again.
EDIT 2: Unfortunately, I can confirm that getting an additional kill does not work.
I got another kill whilst attacking an objective in a vehicle and had the "Armoured Fist" pop-up in the match as if it had been completed. However, on leaving the match there's nothing in my shipments, and the Stug IV still isn't available. It seems we're stuck waiting for the Battlefield team to fix this issue.