In media library, images show in list view, but not in grid view. This becomes an issue because adding a featured image is done by grid view only.

I had to edit the DB to make all jpg files lower case, and changed the actual picture files to match. Everything shows correctly except grid view. New images I upload through media manager show fine in grid view.

The corresponding URL is correct, as expected since the list view shows the image. Plugins on or off do not make a difference.

Various forums have mentioned the same problem, but no solutions. What would be causing this and how to fix?