Autoptimize & WordPress 5.9 issue with aggregated inline CSS

WordPress 5.9 comes with a change I had not noticed before; it is adding inline CSS with random-ish names, which when “also aggregate inline CSS” is active makes the AO cache grow incredibly fast.

As a workaround you can add .wp-container- to the CSS optimization exclusions. I have just pushed out Autoptimize 2.9.5.1 which automatically excludes inline CSS with that string.