The genocide of ethnic Poles (22,000+ genocided?) at Katyn was blamed on Germany by the Soviet Union, but later revealed and confirmed (after the fall of the Soviet Union) to have been committed by the Soviet Union itself. And the Soviet Union had other genocides of ethnic Poles, such as https://en.wikipedia.org/wiki/Polish_operation_of_the_NKVD before WW2 with maybe 110,000 ethnic Poles genocided. The extremely brutal suppression by Germany of Polish uprisings did however include extremely many Polish lives to be lost.

What is strange is that Hitler held a state funeral for Pilsudski and seemed to revere him, possibly in part because of his successful defense of Poland against the invasion by the Soviet Union in the early 1920s. And Germany repeatedly sought defense pacts with Poland in the 1930s, though Germany as far as I know required terms that were unacceptable to Poland (and there was a lot of bad blood between Germany and Poland for many different reasons, including historical).