I think I know what's happening here.
From what I understand, Eyes of Argus whiffed on its last hit because Double fell into it. Thus, as she was pushed up from each hit, she missed the last one. Remember that Eyes of Argus and similar attacks go by a lot faster if they hit nothing. Because it missed the last hit, Double resumed her fall a tad bit early. Since Double hit the ground, the hitstun was cut short, the combo ended, and the game treats the second part of Argus Agony as a new combo, thus why Double didn't block it.
Your combo should still work if you wait a while after the Timpani Drive to use Horn Crush such so that Argus Agony's laser gets all hits. The timing may be tricky, but it should be possible.