Okay, I activate Smush Pro, it smushes away, tells me it's completed its job: total size reduction of 151 MB for a 37% reduction. Excellent!
It also tells me that it is enabled and will smush new images as I add them! Excellent!
Then I go to my plugins page and there is this note: The plugin wp-smush-pro/wp-smush.php has been deactivated due to an error: Plugin file does not exist.
What is happening and what do I do about it?