When will the Yoast SEO problem be solved?

Hi,

It should be solved already, as the mixed content fixer works in a different way now. The warning is still there, but will be removed in the next update.

If the mixed content fixer does not show active in your config page, you can check if it is working by searching for the mixed comment marker in your websource: data-rsssl. For more detailed explanation, see:
https://really-simple-ssl.com/knowledge-base/how-to-check-if-the-mixed-content-fixer-is-active/