One of the chests that I feel people are missing is during the Well Of Dreams act.
There's a point in the game where you have to cross several ledges while trying to avoid tar raining down on you. At the very last one, make sure that you jump below and hit the ledge and then the ground. Head a little bit to the right and there's the treasure chest. I feel like people are missing that one A LOT. That was the one I missed, because I got every other chest (including the two after killing the three archers in Argos) and still didn't get the achievement. So I did another playthrough, using the IGN guide, and finding them all.