VHDL outputs all 'xxxx' for one specific case

Question

My code has to work in 2 modes, mode 0 works without any problems, however mode 1 starting of the fist if statement implemented just shows xxx. all of the values are input manually in the simulation file, so it should not have any dependences on the previous blocks that are used.

library ieee;
use ieee.std_logic_1164.all;
use ieee.numeric_std.all;

entity floor_organiser is

port (mode : in bit;
        route : integer range 0 to 30 := 0;
        cf :in std_logic_vector (2 downto 0);
        df1 :in std_logic_vector (2 downto 0);
        df2 :in std_logic_vector (2 downto 0);
        df3 :in std_logic_vector (2 downto 0);
        df4 :in std_logic_vector (2 downto 0);
        f1 :out std_logic_vector (2 downto 0); 
        f2 :out std_logic_vector (2 downto 0);
        f3 :out std_logic_vector (2 downto 0);
        f4 :out std_logic_vector (2 downto 0));
end entity;

architecture meow of floor_organiser is 

    signal vecup : std_logic_vector (15 downto 0) := "1000100010001000";
    signal iup : integer range 0 to 15 := 15;
    signal orderup : integer range 0 to 15 := 15;
    signal vecdown : std_logic_vector (15 downto 0) := "1000100010001000";
    signal idown : integer range 0 to 15:= 15;
    signal orderdown : integer range 0 to 15:= 15;
    signal aux : std_logic_vector (3 downto 0);
    signal numsup : integer range 0 to 3 := 0;
    signal numsdown : integer range 0 to 3 := 0;
    signal final : std_logic_vector (15 downto 0);
    signal ifinal : integer range 0 to 15 := 15;
    signal finalup : integer range 0 to 15 := 15;
    signal finaldown : integer range 0 to 15:= 15;
    
    constant a : integer range 0 to 3 := numsup;
    constant b : integer range 0 to 3 := numsdown;
    
begin   
    
    process(mode, cf, df1, df2, df3, df4) is 
    begin 
    
    if mode = '1' then
    
        --df1
        
            if cf<df1 then
                vecup(iup) <= '0';
                vecup(iup-1) <= df1(2);
                vecup(iup-2) <= df1(1);
                vecup(iup-3) <= df1(0);
                iup <= iup-4;
                
            elsif cf>df1 then   
                vecdown(idown) <= '0';
                vecdown(idown-1) <= df1(2);
                vecdown(idown-2) <= df1(1);
                vecdown(idown-3) <= df1(0);
                idown <= idown-4;
                
            end if; 
            
        --df2
            
            if cf<df2 then
                vecup(iup) <= '0';
                vecup(iup-1) <= df2(2);
                vecup(iup-2) <= df2(1);
                vecup(iup-3) <= df2(0);
                iup <= iup-4;
                
            elsif cf>df2 then   
                vecdown(idown) <= '0';
                vecdown(idown-1) <= df2(2);
                vecdown(idown-2) <= df2(1);
                vecdown(idown-3) <= df2(0);
                idown <= idown-4;
                
            end if; 
            
        --df3
            
            if cf<df3 then
                vecup(iup) <= '0';
                vecup(iup-1) <= df3(2);
                vecup(iup-2) <= df3(1);
                vecup(iup-3) <= df3(0);
                iup <= iup-4;
                
            elsif cf>df3 then   
                vecdown(idown) <= '0';
                vecdown(idown-1) <= df3(2);
                vecdown(idown-2) <= df3(1);
                vecdown(idown-3) <= df3(0);
                idown <= idown-4;
                
            end if; 
            
        --df4   
            
            if cf<df4 then
                vecup(iup) <= '0';
                vecup(iup-1) <= df4(2);
                vecup(iup-2) <= df4(1);
                vecup(iup-3) <= df4(0);
                iup <= iup-4;
                
            elsif cf>df4 then   
                vecdown(idown) <= '0';
                vecdown(idown-1) <= df4(2);
                vecdown(idown-2) <= df4(1);
                vecdown(idown-3) <= df4(0);
                idown <= idown-4;
                
            end if; 
            
        --ordering vecup
        for i in 1 to 3 loop 
            for y in 1 to 3 loop
                if (vecup(orderup) /= '1') and (vecup(orderup-4) /= '1') then
                    if vecup(orderup downto orderup-3) > vecup(orderup-4 downto orderup-7)then
                    
                        aux <= vecup(orderup downto orderup-3);
                        vecup(orderup downto orderup-3) <= vecup(orderup-4 downto orderup-7);
                        vecup(orderup-4 downto orderup-7) <= aux;
                        
                        orderup <= orderup - 4;
                    end if;
                    numsup <= numsup+1;
                end if;
            end loop;
            orderup <= 15;
        end loop;
        
        --ordering vecdown
        
        for i in 1 to 3 loop 
            for y in 1 to 3 loop
                if (vecdown(orderdown) /= '1') and (vecdown(orderdown-4) /= '1') then
                    if vecdown(orderdown downto orderdown-3) < vecdown(orderdown-4 downto orderdown-7)then
                    
                        aux <= vecdown(orderdown downto orderdown-3);
                        vecdown(orderdown downto orderdown-3) <= vecdown(orderdown-4 downto orderdown-7);
                        vecdown(orderdown-4 downto orderdown-7) <= aux;
                        
                        orderdown <= orderdown - 4;
                    end if;
                    numsdown <= numsdown+1;
                end if;
            end loop;
            orderdown <= 15;
        end loop;
        
        --final vector
        
        for i in 0 to a loop
        
            final(ifinal downto ifinal-3) <= vecup(finalup downto finalup-3);
            ifinal <= ifinal - 4;
            finalup <= finalup -4;
        
        end loop;
        
        for i in 0 to b loop
        
            final(ifinal downto ifinal-3) <= vecdown(finaldown downto finaldown-3);
            ifinal <= ifinal - 4;
            finaldown <= finaldown -4;
        
        end loop;
        
        f1 <= final(14 downto 12);
        f2 <= final(10 downto 8);
        f3 <= final(6 downto 4);
        f4 <= final(2 downto 0);
        
    elsif mode = '0' then
    
        f1 <= df1;
        f2 <= df2;
        f3 <= df3;
        f4 <= df4;
        
    end if;
    end process;
    
end architecture;

The simulation looks like this: simulation