Patzer

His uniform rank was incorrect the entire movie. His rank is that of a Obersturmbannführer, and he was addressed as such a few times in the move. But his uniform rank insignia (collar and shoulder) was that of a Sturmbannführer, one rank lower.

In the film, when Höss learns he will be sent back to Auschwitz, to oversee the murder of the Jews of Hungary, it is the dead of winter, and the trees outside are covered in snow. However, he was actually sent back in the summer, in May 1944.

Topf & Söhne engineer Kurt Prüfer is mistakenly named "Karl Prüfer" in the movie's credits.

At time stamp ~40:59 Dilla the dog can be seen snatching a bite of what appears to be a deviled egg off the picnic table.

In the film, Höss' birthday celebration appears to happen during the summer. Hoss was actually born on November 25. Flowers would not be blooming in November, nor would anyone be swimming outdoors.

When the camera shows Rudolf Höß standing at his office window in Oranienburg, you can see that the window is not from the period, but modern (modern double-glazing and hinges).