It was a custom code issue. In general to troubleshoot such issues try the conflict test below:
- IMPORTANT STEP! Create a backup of your website. Or better approach will be to test this on a copy/staging version of the website to avoid any disruption of a live website.
- Switch to the default theme such as "TwentyTwenty" by going to "WordPress Dashboard > Appearance > themes".
- Go to "WordPress Dashboard > Plugins" and deactivate all plugins except Yoast seo, WPML and WPML add-ons.
- Check if you can still recreate the issue.
- If not, re-activate your plugins one by one and check the issue each time to find out the plugin that causes the problem.
