[Smush Pro] Can't activate the CDN

Since about a week I wasn’t able to activate the CDN on any of my sites hosted with various providers (Digital Ocean, WP Engine etc).

When I click on “Save and Activate” in the CDN tab, the message at the top says there was a success, but the CDN page shows this message:

“CDN is not yet active. Configure your settings below and click Activate.”

I’ve tried sites with just a base WordPress install and smush pro only, still won’t activate. I’ve tried resetting the api connection. I’ve tried reinstalling.