When I have a weapon on me and with a flashlight on and move the gun around in the inventory. The flashlight is automated been taken off weapons. And if I place other stuff on like silence, it's gone totally. And then lost, This might be a bug. 

Having the exact same problem here too

IF you read the posts in the help section you might see that there is a fix for this

If you're using latest version this is intended functionality when stacking guns. If this is happening when moving to empty slots, then again double check your version is latest.

I'm using version 3.4.1 (most recent) and this happening alongside the error in console :

Alright, I wasn't able to reproduce during testing before doing those exact things. Only differences I see are interactions with a skinned item, a skinned container, but the chest is full and the hotbar is full which I don't think I tested full containers and I might not have test with a full hotbar. I'll test more and try to address after work tomorrow. For now setting the disable dupe fix to true should eliminate all or most of those errors. Thanks for providing the additional info, that's probably exactly what I needed.