The reason this happened is because you deleted the field and created it again. This caused the ACF field key reference for any values saved to the field to be incorrect, it points to the old field key that no longer exists. Because of this ACF does not know what to do with the value stored in the database so it returns what is stored without formatting it. The only way to fix this is to update all the field key references, which means that you need to update all posts,
Or you can alter it by doing a query on the DB
UPDATE wp_postmeta SET meta_value = "NEW FIELD KEY" WHERE meta_value = "OLD FIELD KEY"
Please back up your DB before making changes like this.
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