[Risolto] WPML ATE won't load most of the time, or takes minutes to do so

Background of the issue:
I am trying to use the WPML advanced translation editor on my site link nascosto. Since about a week ago, the editor oftentimes won't load the translation job properly.

Symptoms:
The WPML ATE takes minutes to load, and the strings do not appear. Sometimes it loads after minutes, allowing me to edit and save, but often it just keeps loading without showing the strings. In some cases, the error message "Unable to retrieve job details" appears.

Questions:
Why does the WPML advanced translation editor take so long to load?
What can I do to resolve the issue of the editor not loading strings?