WP Smush Pro Plugin Not Smushing Photos

Hello,

I am trying to clean up my site, delete unnecessary, smush photos, etc. I installed the Smush plugin, but it doesn't want to work on this blog. I have the plugin installed on my other 2 blogs and it works.

I went through and deleted all unattached photos, except for my logo image. I am trying to figure out what else could be a problem. I saw another thread with these plugins:

"I'm running WP-Spamshield, W3TC caching, and the Wordpress Photon CDN. Are any/all of these interferring with WP Smush Pro? "

but I don't have any of those. What else could be interfering? Thank you!