As you alreay know the buzz droids are buggy.
You can't apply the new buzz droids (-50% defense and -5% health per turn) if the old ones (0 defense and always a crit) are active.
Once the Vulture Droid is defeated the buzz droids can't be cleansed / destroyed. They are stuck.
This happens in Fleet Arena and the PvE battles (nodes and TB) with both Vulture Droids (The event one and the real one).