WP Smush Pro does not compress manually uploaded photos

Hi ,

My website media just show 28 photos but I have more photos in my upload folder which hummingbird plugin recommend me to optimize them using WP Smush Pro. However, the plugin just keep saying there is 3 files that should be compressed and I repeated the compression many times, but it still gives same message and does not do anything with the other photos. what should I do ?!