hreflang is one of those things that looks simple in the documentation and causes real problems in production.
We manage multiregional websites across the US, Polish, and Ukrainian markets. hreflang implementation issues are the most common reason why international sites lose rankings after migrations, CMS updates, or region expansions. The errors are usually not random - they cluster around the same five patterns.
Here they are, with what actually happens when each one occurs.
1. Missing self-referencing hreflang
Every page in an hreflang set must include a reference to itself.
