On first look it seems some states ( definitely Samara and Nizhny Novgorod ) don't have the Volga river trait despite the river clearly flowing through them. Provinces that have it aren't bordering each other because of that.

Also please add more river traits. Vistula in Poland and some smaller rivers in Central Asia, especially the one in Kokand/modern day Uzbekistan are a must for a map overhaul mod like that.