If you're fighting multiple enemies and you assign your first pet's attack to the space where an enemy used to be very quickly the turn after that enemy died, the game lets you. So if you're trying to defeat a bunch of easy enemies very quickly and you don't wait quite long enough to see if your attacks from the last turn killed that enemy, you can accidentally waste that attack.

I've noticed this lots in the lost grove, but haven't had it happen at all in the festival zone, even when I tried to reproduce the issue there. Idk if it happens in other areas or not.

Are you saying like, in Turn 2, you have all 3 Pets attack the first of 3 enemies. Then, when the turn calculates, the first attack defeats the enemy, but the other 2 Pets attack the, now defeated, enemy as well?

If so, that is intended to work that way.

No, I'm saying in turn 1 I have all three pets attack enemy 1. When the turn calculates, that enemy dies, but because I'm trying to go quickly and didn't realise that would be enough to kill that enemy, I click to assign pet 1's attack for turn 2 to enemy 1 (which is now dead and no longer there). And if I do it quickly enough, the game lets me assign pet 1's attack for turn 2 to enemy 1 who was defeated at the end of turn 1 and isn't actually there anymore.

It shouldn't be able to work that way. It should also error out if the game detects that you've targeted an enemy that no longer exists.

Can you show me like a battle log snippet or GIF of this happening so I can see what exactly you're seeing?

Looking at the battle log, it looks like what's actually happening is that the game is picking one of the remaining living enemies to assign the attack to when you click very quickly on the space where the dead enemy was. So the battle log reads as "[pet] dealt X damage to [living enemy]". So that's good that it's not actually wasting the attack on a dead enemy. However, it still means if there are two living enemies remaining, you didn't get to pick which one that attack targeted.

Is it possible you're just selecting the closest target by pressing '1' repeatedly?

In the Lost Grove, you can select enemies with 1/2/3 hotkeys.

Ohhhhhh maybe. It might be that I press 1 for the first pet's attack, click on the empty space (and nothing happens), then press 1 for the second pet's attack but because I haven't selected a target for the first pet's attack yet, it just takes that as me selecting the first enemy.