The people depicted as condemned in the gas chambers are meant to be Jewish. Yet many appear to be uncircumcised which is contrary to Jewish custom.
The gas chambers, disguised as showers, were always filled with people before the killing operation. In various scenes in the movie however the chambers aren't even half filled.
It is known that in concentration camps, including Auschwitz, all prisoners were shaved entirely, also as part of humiliation. However in the movie when being in the gas chambers many prisoners still have hair.