Voidlings sometimes don't attack Outer Turrets on HA.
No idea why. It only happens to some voidlings, but some of 'em just won't attack the tower even when no other targets are available.
Even if others are around they'll just sit in front of the tower as if they have agro of it, but they won't attack.
They work fine on inner towers on HA and any other structure as far as I can tell.