Crop and Straighten Photos - on a page of several scanned photos

I had the same problem. Turns out my scanner has an "Auto Crop" setting which when active crops the scanned page right to the edge of one or more of the photos. Turning off the auto crop solved the problem. I think PS needs to see "space" around all of the individual photos in order to separate them. So, check your scanner settings and see if auto crop or anything similar appears in the settings menu.

You mentioned that you had provided adequate physical photographs for the function to work. There was no mention that there was adequate tone difference between the edge of each image and the tone separating the images. For example, an RGB mage with a bald sky bleeding off at the edge of the image would present a problem.

As a test, I opened a new file and Lab Color L value (Lightness) criteria in 1 step increments, determined the approximate difference in image-edge tone required for Crop & Straighten to be successful. As the test results below shows a 12 point difference (100-88) was required. This may not translate precisely in all situations (that would require more testing) but it should serve as a useful general guide.

Try clearing your preferences.

Press and hold Alt+Control+Shift (Windows) or Option+Command+Shift (Mac OS) as you start Photoshop. You are prompted to delete the current settings. The new preferences files are created the next time you start Photoshop.