I've set revision = true for a Field Group in its settings page (I tried the same in the Builder for a specific Field, but nothing happened, no revisions were created.).
A revision is made each time I save new Field data, but the revision itself is blank.
Does the revision work with other custom fields? You can also try to define the key WP_POST_REVISIONS in the file wp-config.php to make the revision works. Follow this documentation https://docs.metabox.io/extensions/mb-revision/#notes
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