When I'm in a group and one of the group members has a full backpack, no one else can loot. Our characters are frozen and cannot move. We can loot the chests are appear next to us, but cannot move to loot others. The person who has the full backpack can move and loot, but usually cannot loot all the chests in time prior to the expiration (because the warning text "your backpack is full" is also slowing them down).