Metal slayer question

The sword Metal Slayer.

When you jump in the air and perform an attack combo, it is clear by how the bar goes down that it should do 3 attacks in the air. Yet it only does to, a forward slash and then a spin attack, theres clearly 1 more attack left by looking at the bar yet it never happens? Is it a bug, or is there a special way needed to perform the 3rd attack?