This has happened twice in a row, on two different characters.
Running Earth-crawl Mine scenario where you take the drill to the end of the delve and work your way back to the beginning. After defeating the boss (Maklin Drillstab, I think) the chest spawn as usual, but no gold piles spawn.
Not a big deal, but it is the only time I have had a delve loot stash without ANY gold at all, so I assume it is a bug.