Had this happen to me just now on official UK04, it was starting to get dark and foggy. Once I could not see anything, my inventory looked like this
https://imgur.com/a/KH4z1wv

I experience the same on the latest experimental

It happened on all servers I played on.
The guns effected are:
M4A1
KA-M
MP5-K
UMP45

I tested this a bit further. I went on the UK8 experimental 1person only server. Went to electro harbour. It has two military containers towards the end that can be opened. Upon looting the insides (just one item each) I then moved about 100m away, next to a red container with a bush next to it. I had a clear view of the inside of one container from there. Loot respawned after about 1 to 2min. Furthermore, in most cases I tested this, the spawned loot in both containers was the same. The same loot spawning in close proximity is something I also noted with loot spawed at boats (IV starter kits, flashlights mostly).