Various comments about the commercial load seem to envisage this was just some mainstream scheduled flight. It wasn't. It was a holiday charter.
Everyone on board is known to be on a package holiday from around St Petersburg, and going home.
Such charters carry very little, or more commonly, no freight.
Why do we keep coming back to possible hydraulic leak on rudder? ... It is De-icing fluid residue
Possibly because some very experienced engineers above said that's what it was. Even in Russia, they are unlikely to have deiced the aircraft over the recent summer period, when the photos were taken.