Problem: The client reported that hreflang tags were missing from the XML sitemap for product pages, product category pages, product tags, and blog post categories on their website. Solution: We recommended updating the WPML and Yoast SEO plugins to the latest versions. After updating these plugins on the client's sandbox site, we verified that the hreflang tags were correctly added to the XML sitemap. We then advised the client to update the plugins on their production site and recheck the sitemap.
If this solution does not resolve your issue, or if it seems outdated or irrelevant to your case, we highly recommend checking related known issues at https://wpml.org/known-issues/, verifying the version of the permanent fix, and confirming that you have installed the latest versions of themes and plugins. If the problem persists, please open a new support ticket at WPML support forum.