French translations have many empty results

Without knowing your configuration/ mapped languages it is hard to help in this case.
Since it is working with other languages (other ckeditor fields), the error seems to be somewhere else.

I am seeing the same issue using deepl api. Once in a while the ckeditor 5 rich textarea is empty on the review page. I am mapping English to French with Spanish, Japanese in my languages but only working on French.

Config files are attached. Let me know if you need more.

Drupal: 10.5.2
module: 2.2.12

Just retranslated the same textarea that failed earlier and it happened again. See screenshot.

Tried it again, and the translation appears briefly, then disappears.

Example:

Words to be translated. 

--> translation before disappearing then disappears.

My case has nbsp in the string.

I actually spent a significant amount of time working with DeepL, they wanted postman results confirming it, but there is an issue with their postman collection and I could not get it to work so they would not help.

In the end I reviewed the translation again and realized I did not have plaintext set as an available text format so Drupal was not sending the text up properly.

Sounds like it is a different issue for you.