unexpected Quartus optimisation

Here is the part of code. I don't think you can reproduce the issue as it happens sometime during large project build.

signal counter : integer range 0 to 2 := 0;
-- coefficients
type type1 is array(0 to 13) of integer range -2**15-1 to +2**15-1;
constant polyphase1: type1 := (-10,-56,215,-556,1209,-2527,6966,13025,-2559,939,-319,66,16,-27);
constant polyphase2: type1 := (-27,16,66,-319,939,-2559,13025,6966,-2527,1209,-556,215,-56,-10);
constant polyphase3: type1 := (-56,147,-291,474,-662,804,15552,804,-662,474,-291,147,-56,0);
type type2 is array(0 to 13) of std_logic_vector(15 downto 0);
signal coeffs : type2;
....
....
process(reset,clk)
begin
if reset = '1' then
   counter <= 0;
elsif rising_edge(clk) then
  if counter = 2 then
      counter <= 0;
  else
      counter <= counter + 1;
  end if;
  for i in 0 to 13 loop
     case counter is
        when 0 =>        coeffs(i) <= std_logic_vector(to_signed(polyphase1(i),16));
        when 1 =>        coeffs(i) <= std_logic_vector(to_signed(polyphase2(i),16)); 
        when 2 =>        coeffs(i) <= std_logic_vector(to_signed(polyphase3(i),16)); 
        when others => null;
     end case;
  end loop;
    
end if;
end process;