When you convert labels to annotations, a new annotation group is created in map document.In layout view, annotations can be moved or edited when you Focus Data Frame (small dashes appear around data frame) by double clicking inside data frame or using button of Layout toolbar.When you copy and paste an annotation in Focus Data Frame mode, this annotation should be visible below original one. But by default it's not placed in the same annotation group as original annotation but in <Default>. It can be changed in Drawing toolbar: Drawing menu -> Active Annotation Target. It should not cause your problem but introduces a mess in annotations.It's also possible, but undesirable, to copy an annotation in Focus Data Frame mode and paste outside this mode, in normal layout view. Then usually annotation text is not visible. So make sure you copy and paste annotation in Focus Data Frame mode and to proper targed annotation group.
