Mate had the same problem as you. tried everything, brand new master, bias valve and vacuum, blew out lines, bled many times using foot and also vacuum bleeder. turned out that one of the brake pistons was sticking. wouldnt move when bleeding, but would when under pressure. caused similar issue to what you have.
also take out your bleed nipples and make sure the holes in them are not clogged (ive had this one myself)