The recent geomask service introduced a little regression in the code, resulting in group attributions being ignored.
The issue is located at https://github.com/nyurik/wikimedia-mapdata/commit/131284194cda7a00b36e6b22cb90e519cbf38a29#diff-3143c0ec6f660badf4d52ad8bc373a6eR104 where service is removed from the GeoJSON data.
parseAttributions relies on it so it's become no-op.