There is sometimes a huge gulf between what is actually "historically accurate* and what a governement perceives or wishes to represent as accurate.
This is especially true in what could be perceived as somewhat repressive contries.
The Russian government for almost the entire existence since the Revolution has wished to be perceived in the best possible light and has restricted and attempted to mitigate any actual or perceived criticism of itself or it's administration and legal systems regardless of whether they were valid then or now.
On 15 April 2015, the Russian film distributor Central Partnership announced that the film would be withdrawn from cinemas in Russia, although some media stated that screening of the film was blocked by the Russian Ministry of Culture. The decision was made following the press screening the day before. The Ministry of Culture and the Central Partnership issued a joint press release stating that the screening of the film before the 70th anniversary of the Victory Day was unacceptable.
The Ministry of Culture claimed that it received several questions on the film's contents, primarily concerning "distortion of historical facts, peculiar treatment of events before, during and after the Great Patriotic War and images and characters of Soviet people of that era". Russian minister of culture Vladimir Medinsky welcomed the decision, but stressed that it was made solely by the Central Partnership.
However, in his personal statement Medinsky complained that the film depicts Russians as "physically and morally base sub-humans", and compared the depiction of Soviet Union in the film with J. R. R. Tolkien's Mordor, and wished that such films should be screened neither before the 70th anniversary of the victory in the Great Patriotic War, nor any other time.
Arguably, since the movie is a fiction and only loosely based on a events it cannot be considered a depiction of actual events but nevertheless, the Russian government sees it as an slight on the character of the Russian governement &/or country &/or it's citizens.
PERCEPTION is something I have mentioned several times and that is key here. It's how the Russian government wishes to be perceived and, apparently, has the necessary will and muscle to enfore it...if one sees the withdrawl of the movie as a "ban".
Just to add....
Comment from @Galliifreyan
...the original book was based loosely on the story of a real serial killer Andrei Chikatilo, and the USSR spent an outrageous amount of resources (including military helicopter patrols and some millions of rubles) to find and capture him. The premise that USSR denied the existence of murders and did not do anything to prevent them may indeed seem a bit offensive in this context.