I have fought with Wealth omens during one of the Prey event
tons of loot- gold, legendaries, few uniques and alot of rare items were dropped
but in the process of killing new waves of omens and dropping new items-previously dropped items began to disappear
When the event has been done there was only few rare items left on the floor
This happened to me twice - on lvl 58 and today on 69 during regular 80ish difficulty map blasting

i've experienced many bugs in this game since release but none was quite a blow like the vanishing loot after the fight with omens
which are not easy to kill in such numbers with certain builds

Looting and gearing up is the essence of arpg games so please! take a look on that one as soon as possible!

Thank you in advance