The poster of that other thread used the term “item name” to refer to the label that’s on the ground, which is separate from the tooltip you were able to see. My response there is a bit confusing-- the Z key is supposed to disable the labels on the ground, not the tooltips you see when hovering. There could be a bug specific to uniques that causes the text to be hidden but for the label to still exist.
In any case, if you have this happen again and the Z key is not the cause of the problem, a log file would be helpful.