Ammo loaded into the pistol grip shotgun (which was in my hands whilst jogging/sprinting) randomly disappeared.
Noticed the message in the top right change to red to indicate no ammo loaded and then when I checked the weapon the ammo was gone (ejected?)
Have tried to replicate but it seems to be random.
You dropped the weapon at some point, and it sort of "duped" meaning it is visible for certain players. Now, they can't pick up the shotgun (usually) but they can take out the ammunition out of it.
I had that happen to me this morning. It was only a kilometer away since I last dropped the gun, so I knew there was a guy there. Went back, shot two dudes, took my ammo back.