I am playing a PBEM (2 player version) as Austrian side, ROP Gold v. 1.11 - the latest version on Steam.
In early July 1757, a huge Russian army enters in the Polish region of Wierzbolow. However the region is labeled locked and impassible, so the Russians cannot do anything further. This is just after the "Shall Danzig Remain Neutral?" choice event has fired and the other Russian forces appear as well to lay siege to Memel. I looked in the forums, and apparently there was much back and forth about this bug. Apparently the events files for 1757 are the issue.
Was it ever fixed?
I have a hard time believing the August 20, 2016, Steam version has a old unfixed game killer like this. Do the units or region unlock later? Am I missing something?