Missing reciprocal hreflang (no return-tag)
This means that the URL in question has hreflang annotations where at least one of the alternate hreflang URLs does not reciprocate.
Why is this important?
Hreflang tags are interpreted by search engines as indexing instructions. Search engines can follow and understand hreflang instructions if they are valid, consistent and reciprocal.
If an English page has hreflang pointing at its French alternate, the French page must also have hreflang pointing at the English page. If this return tag is missing, search engines will ignore the hreflang instruction.
What does the Hint check?
This Hint will trigger for any URL which has outgoing hreflang, where at least one of the alternate URLs does not reciprocate.
Examples that trigger this Hint:
Consider the URL: https://example.com/en/page-a/
The Hint would trigger for this URL if it had outgoing hreflang;
where the URL https://example.com/fr/page-a/ would have hreflang;
but no reciprocal link back to the /en/ page.
How do you resolve this issue?
Hreflang must be reciprocal, so this is an issue you cannot ignore if you want hreflang to work properly. You will need to add the missing hreflang for each page which does not reciprocate.