When Alexei Kardakov confronts Svetlana Sorokina, the blood on Svetlana's upper lip noticeably changes (even disappearing and reappearing at one point) between different shots.
In the scene when Svetlana refers to her flat and is attacked by Kardakov, she has blood all over her upper lip. But when Kardakov hugs her, she has only one little blood spot on her upper lip.
At the May Day protest, multiple protesters can be seen waving banners for Antifaschistische Aktion (Antifascist Action), but this organization did not exist until 1932 - two or three years after the setting of this episode.
U-Bahn (underground) platforms are shown bearing tactile paving for the visually impaired. This was not introduced before the 1990s.
In the Homicide office, the chairs are Thonet's S 43, designed by Mart Stam. They were introduced in 1931.