So I had my thumbnail width down to like…100 pixels…hence, they were blurry. Moved that number to 300 and everything is now fine.
I had this happen too. It was a conflict with another plugin. In my case it was AutoMinify. As soon as I disabled that WP Optimize worked perfectly.
Any overlap on compresison or header work will break the site. SO remove all other plugin related to caching or speeding up your site before layering them back in,
