Page Not Found

Hi! After installing this plugin, I still received the “Eliminate render-blocking JavaScript and CSS in above-the-fold content” error. So, I ticked inline and defer option in autoptimize and pasted the critical path css into the textbox. When I click save and clear cache, the page loads with the following error:

“Oops! That page can’t be found.
It looks like nothing was found at this location. Maybe try one of the links below or a search?”

Any idea what went wrong? I do use WP Fastest Cache, but I made sure to disable the minify settings so as not to conflict.

I used the following url to create the critical path to paste in the box:
https://jonassebastianohlsson.com/criticalpathcssgenerator/

I am also using a child theme, would this impact things as well?

Thx much!!