Ryan Labelle

Sharing my solution until a proper fix is applied. If you are having the same issue, add this to your funcitons.php file.

//-----------------------------------------------------
// WordPress Importer - Skip Duplicate Meta Keys
// Helper function to prevent addition of meta keys if
// already exists.
//-----------------------------------------------------
add_filter( 'import_post_meta_key', 'themo_import_meta_key', 10, 3 );

function themo_import_meta_key( $meta_key, $post_id, $post ) {
		$key = $meta_key;
		$themeta = metadata_exists( 'post', $post_id, $key );
		// If key does not exist, add it.
		if(!$themeta) {
			return $meta_key;
		}
		// else skip adding it.
		return false;
}