I had a user today who could not tag or see spaces. He had everything on in the model and the linked model, the worksets were good, and everything he tried... failed.
The problem was the cut plane of the view range was set to 14'-4" because of the strange composition of the building. The architects room objects along with the spaces topped out at 8'-0". When we dropped the cut plane down to intersect the spaces... Wa-shaw! there they were after all.
The solution that works best for us is actually to make the top of all the spaces reach for a new level we added above the whole building. None of the spaces actually get there because they all hit room bounding structure before they got there.