Simulation Failed: Transactions not in Ascending Order GHDL

I'm trying to run a testbench and when I attempt to run the simulation I get the following error:

./rc_symbols_testbench:error: transactions not in ascending order

./rc_symbols_testbench:error: simulation failed msf_symbols.vhd rc_symbols_testbench.vhd

A reduced version of the testbench that still produces the error:

library IEEE;

use IEEE.std_logic_1164.all;
use IEEE.numeric_std.all;
use STD.textio.all;
use IEEE.std_logic_textio.all;

entity rc_symbols_testbench is
end;

architecture impl of rc_symbols_testbench is

    subtype byte is std_logic_vector(7 downto 0);
    constant byte_null: byte := (others => '0');
    constant byte_unknown: byte := (others => 'X');

    constant clk_freq:   integer := 25500;
    constant clk_period: time      := (1 / (clk_freq))*sec;
    constant gate_delay: time      := 0.1 ns;
    constant t_sample:   time      := 100 ms;
        
    signal   eod:         std_logic                       :=            '0';
    signal   clk:         std_logic                       :=            '0';
    signal   rst:         std_logic                       :=            '0';
    signal   dcf_tro:     std_logic                       :=            '0';
    

begin

    process
    begin
    
        while eod = '0' loop
            clk <= not clk;
            --wait for clk_period / 2;
            wait for 19.60784314 us; --19.6us approx = clock period / 2
        end loop;
        
        wait;
    end process;
    
    rst <= '1', '0' after 150 ms;

    process
        file     data_file:   text;
        variable data_line:   line;
        variable dcf_do_var:  byte;
        variable dcf_tro_var: std_logic;
        variable dcf_so_var:  std_logic;
        variable msf_do_var:  byte;
        variable msf_tro_var: std_logic;
        variable msf_so_var:  std_logic;
        variable t_var:       time;
    begin
        file_open(data_file, "rc_symbols.dat", read_mode);

        while not endfile(data_file) loop
            readline(data_file, data_line);

            hread(data_line, dcf_do_var);
             read(data_line, dcf_so_var);
             read(data_line, dcf_tro_var);
            hread(data_line, msf_do_var);
             read(data_line, msf_so_var);
             read(data_line, msf_tro_var);

             read(data_line, t_var);

            if t_var > now then
                wait for t_var - now;
            end if;

           
            dcf_tro <= dcf_tro_var, '0' after clk_period;
           

        end loop;
        
        file_close(data_file);
        eod <= '1';
        wait;
    end process;

end;

I've also reduced rc_symbols.dat to:

00 0 0 FF 0 1 1736901.960861734 us
00 0 0 FF 0 0 1736941.176548008 us
0C 0 1 FF 0 0 1754705.88243013 us
0C 0 0 FF 0 0 1754745.098116404 us
0C 0 0 31 0 1 1837019.607919256 us
0C 0 0 31 0 0 1837058.82360553 us
00 0 1 31 0 0 1854823.529487652 us
00 0 0 31 0 0 1854862.745173926 us
00 0 0 00 0 1 1937137.254976778 us
00 0 0 00 0 0 1937176.470663052 us
00 0 1 00 0 0 1954901.9608589 us
00 0 0 00 0 0 1954941.176545174 us
00 0 0 00 0 1 2037215.686348026 us
00 0 0 00 0 0 2037254.9020343 us
00 0 1 00 0 0 2055019.607916422 us
00 0 0 00 0 0 2055058.823602696 us
00 0 0 00 0 1 2137333.333405548 us
00 0 0 00 0 0 2137372.549091822 us
00 0 1 00 0 0 2155137.254973944 us

To me, it looks like everything's in ascending order so I'm still not sure.

If I comment out this, it simulates, but I'm not sure how to fix the error:

dcf_tro <= dcf_tro_var, '0' after clk_period;

Thanks to user1155120 for the helpful comments.

The issue lay in the fact that:

constant clk_period: time      := (1 / (clk_freq))*sec;

was evaluating in such a way that it caused a zero or negative delay. Substituting this line for:

constant clk_period: time      := 39.2157 us;

fixed the issue.