[WP Smush Pro] Image compression worse after smushing

Our files are stored moved off to Amazon S3 after a little while, and in order to smush them I had to move them back to the server. Once I moved them back, the smushing ran and succeeded, but after a few days of moving the smushed files back to S3, our image compression score is now even lower than it was before! How do we handle smushing files on S3?