Web stories editor appears blank

In that case a few follow-up suggestions (for your staging/development site):

• Try passing it through json_decode as well to see if PHP can parse it.
• Temporarily disable all other plugins while doing further testing
• Make some temporary modifications to https://github.com/GoogleForCreators/web-stories-wp/blob/ecb5070157c9eb726c7301fbfe497f0391a5aeb4/includes/REST_API/Stories_Base_Controller.php#L137-L140 to add some logging/debugging statements, to see if $post->post_content_filtered is not empty and to see if $data['story_data'] is not empty either.

As I said before, there isn’t much we can help from the outside. So if nothing else works, I recommend restoring a backup from an previous date where everything was still working, and continue from there.

Thank you for your suggestions. Your guidance helped me to fix the issue.