[Closed] Translation disappears after updating the translation

Background of the issue:
We have built a website with the Gutenberg editor and our own custom theme (with ACF fields) and we use WPML for the translations. Our client uses external translators who add content themselves. The translators have added the translations via the ATE. Our client goes into the translated page itself to make some visual changes.

Symptoms:
Once everything is done, when you go to the translations again and save them, the page loses most of the translations and is back in the default language.

Questions:
Why do translations disappear after updating the translation?
How can we prevent the page from reverting to the default language after saving translations?