Has happened to me for multiple reasons before the latest patch, but for the current one it has occurred during log in as well as after trying to reload with the Y button, I’ll have a magazine visible in the gun ( has happened with the SVD & AK) but there’s no magazine in the mag slot in the inventory, have been able to fix it on occasion by opening the inventory & dropping the magazine directly from the gun (if the mag has ammo in it, it will turn to 0 once dropped on the floor & it no longer allows the magazine to be picked up) & then opening the inventory & reloading from the inventory screen. Another one that occurs during log in it will empty the once full magazine & leave a single bullet chambered & you need to drop the mag from the mag slot or the gun will become stuck with 0 Ammo & unable to reload at all ( the mag becomes unusable after dropped). For the most part this bug isn’t as common as it was in previous patches but can be quite frustrating losing ammo/magazines or the full gun randomly. I couldn’t tell anyone exactly how this bug occurs other than from my experience, hope this helps :)