Revit Revision Bubble Not Appearing?

This is so simple, I debated not posting about it. But because this is the second time this same thing got me, if for no other reason it will serve as a note to myself.

A new user came to me, and could not get the revision clouds to appear. As usual, I went through the "how revisions work" speech, and corrected the revision schedule, which was in fact incorrect.

After feeling pretty good about the quick fix, I went to place her bubble, only to get this error:

"None of the created elements are visible in Floor Plan: XX view. You may want to check the active view, its parameters, and visibility settings, as well as any Plan Regions and their settings."

Ok - another simple fix...  obviously my revision clouds are unchecked in the annotation categories tab, of my Visibility Graphics Dialog. (VG -> Annotation Categories -> Revision Clouds).... But, its checked?!

After turning on all the model categories, it worked. Then a minute or two of scratching my head.. I knew it wasn't a workset issue, or a view range issue... I remembered this got me before... The model category "Lines" was unchecked for that view. Click that back on, and everything comes in