Failed to load content CSS

Hi,
while customizing the theme “Customizr Pro” I’ve got to an error saying:
“Failed to load content css: https://www.poderesortoiano.it/wp-content/themes/customizr-pro/addons/wfc/front/assets/css/dyn-style.php?is_customizing=false”.
I’d like to know why this error shows up. Is it an error due to the theme or to a plugin?
Thanks in advance for any reply.

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