Nonresolved signal has multiple sources

According to your diagram, the right code is (without the double register)

if rising_edge(clk) then
  if Rst_n='0' then
    cs <= '0';
    cr <= 0;
  else	
    cs <= ns;
    cr <= cr + muxo;
    --cr <= nr;
  end if;
end if;

         
if rising_edge(clk) then
  if Rst_n='0' then
    cs <= '0';
    cr <= 0;
  else	
    cs <= not cs;
    if cs = '0' then   
      cr <= cr + D_in;
    else   
      cr <= cr - D_in;
    end if;   
  end if;
end if;