Might be another plugin causing it. Try disabling your other plugins to see which one.
Viewing post in Multi Wave Battle plugin - RPG Maker MZ comments
Tried that, but it still shows the enemy from the previous wave (if I use the recover all, even if the recover all only is directed to the enemies at the current wave). And when I don't apply the revive all, then it doesn't show the previous enemies but it still kills all the enemies in the next wave