Would adding another `is_serialized` check help to avoid updating every meta record in the db?
```php
if ( is_serialized( $row->meta_value ) ) {
    $row->meta_value = @unserialize( $row->meta_value );
    if ( is_serialized( $row->meta_value ) ) {
        $row->meta_value = @unserialize( $meta_value );
    }
    // update_metadata will serialize it back
    wp_stream_update_meta( $row->record_id, 'author_meta', $row->meta_value );
}
```
Reference: wp-includes/functions.php:252-256