This has happened several times now to me while playing a group dungeon. I thought at first it was a fluke, but it seems to be a consistent problem.
My group likes to look at everything, read everything, talk to every NPC and empty every sack, crate etc as we go during these events. However if we do a second dungeon on the same occasion, there's nothing in any of these containers. It's also happened part way through a dungeon that suddenly none of the containers had any contents. Fortunately, bosses still do drop appropriate gear, but it's still very disappointing for those of us who like a 'lore and exploration' approach. Books & letters can still be read.
Dungeons this has happened in include: Moongrave Fane, Frostvault and Scalecaller Peak, but there have been others.
It seems to happen that anyone who has just joined the group without doing the first dungeon can still find items in the group-as-a-whole's second dungeon, but for those of us who have completed one there just isn't anything there. I have no idea why this should happen, but it's frustrating so getting this sorted would be great if that's possible, please.