After ControlDraw displays a diagram it stores an image of the each diagram in the model, so that next time it is shown it does not need to redraw the entire diagram from scratch, and so that the reviewer can show them.
These images can more than double the size of a model. Shrinking a model removes them.
During a complete update these images may also be removed.
After shrinking a model then it will automatically rebuild page by page as pages are opened.
You can force them all to rebuild, so making the entire model available in the reviewer by >View >Page browser or by clicking the button in the list of diagrams