1.) I had a Shotgun in my inventory that disappeared. I thought I dropped it but when I went to add a sight to another gun it gave me the option to add it to my Shotgun that was not there and when I did add it to the Shotgun the sight or attachment vanished.
2.) for some reason the game was attaching ammo or other items to things like the medkits, or gun attachments I thought I lost ammo I went to my medkits and it gave me an option to remove attachment and 400 rounds of rifle ammo was attached to my medkit.