I noted this bug appearance on these occasions
I. In arsenal when you change weapon while reloading.
II. When trying to reload your weapon while climbing a ladder.
III. Happend to me in Adapt campaign today I am not sure what caused it though.
IV. Happend to me again when I randomly grabed a new weapon this time in multiplayer.
I. Arsenal
1.Go to Arsenal
2.Grab a gun
3.Reload it
4.Quickly change your weapon while reloading
5.Try to reload
II. Ladder
1.Go to editor
2.Spawn near a building with a ladder
3.Start Climbing up/down
4.Reload
5.Stop climbing and try to reload your gun
It used to happen prior FFV update on devbranch when you pressed reload more then once.
Just tested and it is 100 % reproducible in VA when switching weapons while the reload animation still plays. Afterwards all magazines vanish when reload is pressed, or when dragging and dropping a magazine on the magazine slot of a gun in the inventory screen. Sidearms and Launchers are also affected.
Use a gun with a long reload animation (MG, sniper rifle) when attempting to reproduce it.
Related to #22942
I had this occur twice in missions using 1.40RC branch. First time it occurred immediately after using a first aid kit during a TPW fall animation. It didn't just affect reloading, I was unable to put items into my inventory from ammo boxes or dead bodies without them disappearing.
Reverting to an earlier save, restarting ARMA 3 or restarting the PC did not resolve the bug.
I had this happen to me during multiplayer a few times, weapon would reload a new magazine, magazine icon would be visible in the inventory UI, but the magazine had no ammo left in it. Reloading again would cause the next magazine to be empty too, until no more ammo is left.
No idea under which circumstances this happened. I have no way of reliably reproducing it.
Had this in vanilla campaign several times. I'm not fully sure, but it seems that messing up with your inventory in an overly perfectionistic way may somehow affect that.