@ZOS_GinaBruno This is happening on x64 PC client as well. It happened to me twice on treasure map chests, and when I log back in the chest is gone, as is my map.
I had the same problem with my Macbook pro crashing while looting after the Thief DLC patch. I turned off the auto loot and seems to be working fine now. HAs something to do with the autoloot script on MACs, also running at Ultra High performance. Hope they get a patch fix soon.