SelectFaction = RUS
EvalRgnOwned = $Mazowsze
As written it lacks the select faction for that test so the event files - just add the Rus line beneath conditions.
Same mistake for:
In combination this will make the early 1860s very uncomfortable for any Russian player ...
Edit: Also take out the lines for no Polish control, the target region is Warsaw and all that does is to complicate the process - remember the PoN event syntax is not very good at 'and' or 'or' type rules