Hello!
Could you please provide a temporary access so that we can check your site?
The issue that you report might indicate a corruption of a sort of the database. Of course, it is too early to give an exact cause for this and it will be determined once we have more details.
There is an issue with the Classic block on the post. If I click on Convert to blocks > Save post > Update the translation. Then the post content is available in Advanced Translation Editor as well. Please check this screenshot hidden link