Press F5 to refresh thumbnails. Or
Try pressing Ctrl+A (to select all) and then refresh again (Edit à Update Thumbnails). If that makes no difference you may need to regenerate the cache.
1. Close Organizer.
2. Navigate to C: ProgramData/Adobe/Elements Organizer/Catalogs/My Catalog
3. Find the file - thumb.5.cache
4. Highlight the file and delete it.
5. Re-start Elements Organizer
6. Wait until all thumbnails have been generated.
N.B. your catalog is normally called “My Catalog” if you have chosen a different name (it will be shown bottom left of the Organizer) navigate to the appropriate folder.
ProgramData may be a hidden system file: