Hi.
There are a issue in the new MB Revision plugin, which all headings become revision values too, and would show the whole revision array as JSON.
I solved the issue by add a type check in class-mb-revision.php in line 155:
if($field['type'] == 'heading') return;
Just in case you would like to follow up on the issue, and fix the bug 🙂
Best
Troels