[Risolto] Translating 404 error page from Elementor Theme Builder doesn't close after saving

Background of the issue:
I am trying to translate my 404 error page from Elementor Theme Builder on my site link nascosto. I am following the normal translation procedure using the Classic Translator.

Symptoms:
The translation process gets stuck. One of the elements, a header with '404' in it, is not appearing for translation. Clicking 'Save and Close' saves the translations, but the screen does not close and return to the list.

Questions:
Why does the translation process get stuck when translating my 404 error page?
Why is the header with '404' not appearing for translation?
Why does the screen not close and return to the list after clicking 'Save and Close'?