This thread is resolved. Here is a description of the problem and solution.
Problem:
If you're experiencing issues where the language-changing option is not appearing on some pages,
Solution:
We recommend checking if the pages in question are translated. The language switcher only appears on pages that have been translated. Once you translate the page, the language switcher should appear correctly.
If this solution does not resolve your issue, or if it seems outdated or irrelevant to your case, we highly recommend checking related known issues at https://wpml.org/known-issues/, verifying the version of the permanent fix,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. Additionally, you can open a new support ticket for further assistance at WPML support forum.
This is the technical support forum for WPML - the multilingual WordPress plugin.
Everyone can read, but only WPML clients can post here. WPML team is replying on the forum 6 days per week, 22 hours per day.
This topic is split from https://wpml.org/forums/topic/header-and-footer-disappearing-when-switching-languages-on-website/