My scenario has an M2A4 Slammer UP tank with a crew of 3 units. If these units are AI, everything is fine; as soon as these units become players the tank commander having fired at least one shot from his machine gun, will receive a change in his weapon stats (+1 magazine for machine gun, + 1 smoke screen magazine) see screenshot

If this player leaves the commander’s seat and comes back (or another player sits in the commander’s seat), then the loaded magazine will have 0 rounds and it will be possible to load a new one, and all smoke screens will disappear

This shot

by commander was made immediately after starting the game, if you wait a few seconds and only then fire the shot, the bug will not be reproduced
Also I note this 'Canon 120 mm' text initialising some time in MP (all tests was on Dedicated server)

Well,

this can be reproed with AI gunner too but some other behaviour
See YT video https://youtu.be/JjSzRUrEaOE: the 1st attempt give me a full worked Smoke Screen duplication and +1 magazine for machine gun; 2nd attempt just removed all smoke

Pleace note

player crew can get this bug even if commander do not have any weapon (only Smoke Screens), but I have not 100% repro for this situation, only for up ones