[Закрытые] English showing up on French pages

Background of the issue:
We are working on a project to upgrade a site from an old version of WordPress and WPML on a default French site. We upgraded from WordPress 4.x and WPML Version 3.8.2 to WP 6.6.2 and WPML 4.6.13. At one point there was a message that the .MO files needed to be created. We found that the folder was missing (/wp-content/languages) and then it was able to regenerate the .mo files, fixing about 50% of problems with English text on the French pages. When we went to WPML -> Support -> Troubleshooting and clicked the 'Show custom MO Files Pre-generation', it asked again to regenerate the .mo files. The process completed, but we did not notice any more of the problems with the wrong language on the site getting fixed.

Symptoms:
Certain text is appearing in English on some pages of the default French site.

Questions:
How can we find out what is causing the English text to show up on the default French section?