[Smush Pro] Smush keeps saying we have 21 images requiring smushing

We installed Smush and bulk smushed all the images. But after the process was completed, it said that we have 21 images that need to be optimized.
So, we smushed them again and it said that all images had been smushed. We clicked the “Re-check images” button and it again said that we have 21 images needed to be smushed.
We did the same for a couple more times with the same results and it seems we’re going in circles.
Please advise.