With cropped views, you usually run into problems in two circumstances: having your crop-sketch associated with the wrong view and having too many views int he drawing.
You can tell if the first situation is the case by expanding the view in the drawing tree and seeing if it has a crop icon on it. If that's the case, delete the crop, double-click the view view you want to crop, redraw it and recrop it.
The second situation applies to just about any derived view type. When you start going over 20 or so views in a drawing, section, detail and crop views will begin to drop out.
Combining crop and broken views can cause components to drop out. Usually the answer is to edit the crop sketch and then exit out of it.