A protocol mismatch that broke every hreflang annotation

A protocol mismatch that broke every hreflang annotation

Hypothesis: an HTTP/HTTPS mismatch in hreflang URLs was invalidating annotations sitewide post-migration. Methodology: forensic, post-HTTPS-migration. One site, ~8,000 URLs, where the canonical and on-page content moved to HTTPS but the hreflang annotations still listed http:// URLs. 8-week recovery.

Findings:
— Google treats http:// and https:// as different URLs. Every hreflang entry pointed to an http URL that now 301-redirected to https — so every annotation referenced a redirecting, non-canonical target.
— Result: the entire annotation set was effectively non-reciprocal. GSC 'no return tags' errors spiked to ~7,600 within two weeks of the migration.
— Correct-country serving across all markets fell ~15 points in the same window — a sitewide, not market-specific, signature, which is the tell for a protocol/host-level bug.
— One template fix updating all hreflang URLs to https. Errors cleared to ~90 in 4 weeks; serving recovered.

Caveats: forensic case, recovery confounded with normal post-migration stabilization. But the sitewide-uniform nature of the drop strongly implicates the protocol bug over content factors.

Conclusion: hreflang URLs must be absolute, canonical, and protocol-exact. After any HTTPS or domain migration, re-audit the annotation URLs themselves — not just the pages they sit on. This is the most common post-migration hreflang failure we encounter.