HTTPS is invalid and might prevent it from being indexed

I think there are index problems due to Http:// in theme files. For example :
http://schema.org
http://www.w3.org/2000/svg

No, this is not your problem.

These are NOT resources loaded on your site, and shouldn’t cause any HTTPS/mixed-content errors. They’re merely pointers to external technical specifications.

To explain this further, let’s say you have a paragraph of text, and in this paragraph, you have a hyperlink to the URL http://www.example.com, like This is an example.

Yes, this is HTTP, but you’re NOT loading or embedding the resource or content on your site: you’re merely linking to the URL. And mere links should NOT create a mixed content error.

As to the GSC error itself, please take a look at Google’s official support article here: https://support.google.com/webmasters/answer/11396518

Good luck!

 

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