When One door Closes loot bug?

Message is: " You are not allowed to loot the item <various items>"
No reason given (eg they do not already have the item). Not all in the group affected. Tried leaving on corpse then looting, same message.
Done this mission many dozens of times, not seen this before

Did the looter drop the mission before looting? That's the only time I've seen that happen.

Old Bug. If you are dead on the win it can bug and not give you credit for the win which blocks you even if you drop the exp and get readded to it.

Can happen also if you are zoning at the instant of the win.