During the 2018 Gdynia Polish Film Festival, 'Kler' was met with the longest applause of the audience which should have given it the Zloty Klakier (Golden Clapper) award, presented each year by public Radio Gdansk. However, the Managing Director of Radio Gdansk decided not to award any movie with Golden Clapper that year, citing 'an impossibility of objective assessment of survey accuracy' as a pretext . Commentators have connected it with the controversial subject of the movie, which was criticized by the part of ruling politicians in Poland, who decide about manning of the public media.

A character of archbishop Mordowicz and many of his personal traits (swearing, heavy drinking, fondness of accordion music and luxury, treating of subordinates) are patterned upon known nonpublic behaviours of archbishop of Gdansk, Slawoj Leszek Glodz.

Scenes of violence against children and child abuse in nuns' orphanage are based upon real events from so-called sister Bernadetta's orphanage in Zabrze, revealed a couple years before filming.

A character of a priest, organizing meetings of extreme rightist hooligan groups, is patterned upon real priest (now former one) Jacek Miedlar, accused of hatred crimes.

Two of the characters - Trybus and Lisowski - are named the same as two characters from Drogowka of the same director.