Then it has to be in your crossover or connection to the tweeter. You have inspected the crossover and they LOOK identical. Triple check that. Then put on some music, softly, and wiggle each connection in the bad crossover (looking for a bad solder joint). If that doesn't revel the problem, step away for a day and try to get another pair of eyes on the crossover comparison. We tend to look for problems the same way, in the same patterns. Someone else will approach it differently.