If you kill a turret but then die right after, or if your arsonistic chip kills a turret while you are dead, the game will prevent you from looting while you are dead. (Turrets have some kind of built in auto loot, possibly similar to instances?)
However, once you revive, the mob is there and shows up as lootable on the radar, but you are unable to loot the turret, either manually or with a loot pill. I’m not sure if this is an issue only with turrets or also with mobs.
It happens with mobs too.
Same happened to me idk how I even killed it but also died by it without an arson ?
Almost lost a 30 ped mob to this bug, but tried relogging and it works.
So, seems relogging will allow you to loot, as a workaround for now.
But hopefully MA sees this and can fix it.
Also 3 minutes to loot mobs in some cases is too low amount of time and it should be increased to at least 5 minutes.
Okay…just kidding, workaround may or may not be worth it depending on your situation. I got locked out of the boss room when I relogged 
same happened for me, the mobs too