More pictures than visible. Where are these

[View this post in your web browser. It contains formatting and images that don't appear in email.]

Building on Conrad’s answer:

1. Go to Library.

2. In the Catalog panel in the left column, select All Photographs.

3. Turn off Library filters by ensuring the menu item Library > Enable Filters is unchecked. (See the menu item for the keyboard shortcut.)

3. Do the menu command Photo > Stacking > Expand All Stacks.

Are any Library filters active, hiding some photos or videos? Filter status is shown in the middle of the window at the top, but the posted screen shot does not include that, it shows only the left side.