I have had several experiences wherein an invisible enemy is the only one within range of an attack, and yet they are still listed as unattackable. This has been an issue with the water elemental sin the new Explore areas, and I just had it happen with another enemy. Specifically, the wizard with the lightning staff could not attack the only enemy in range during a Challenge in the Anvil of a Dumathoin area.
I have noticed this off and on since the update that added the new Explore areas, and I think I have finally figured out the exact bug. Can someone help me confirm?