@Mira995 Yeah, it really doesn't make any intuitive sense. As I recall (and others have noted), it should be 3 times
per body. Likewise, (as others in the comment section have also already taken note of) since the ant would presumably have the healing ability as well (as it had just been clarified only a moment earlier that the ant had absorbed the power), your guess is as good as mine on why he didn't attempt it first on the ant. Instead of, y'know, potentially eternally damning the soul of a well-considered individual. :S
@demondiary and
@Le_Flemard guessed that it had to do with the higher failure chance on the ant [as the failure rate increases based on the strength of the opponent, relative to the shadow lord], but there would have been plenty of time to attempt it with the ant while his shadows were searching for the healer.
Thus the only thing I can assume is that he's deliberately delaying raising the ant until he can apply some sort of boost to maximize the odds for it (which would be awfully cold in regards to needlessly putting the female hunter's life at continued risk) or that (in a fit of emotion-fueled anxiety completely contrary to what we've seen of his character so far) he simply forgot the ant existed in his concern over the other hunter (despite having literally just taken it down a few seconds prior). Well, regardless of what we go with, it'll feel like a stretch. May as well just assume necromancy-induced dementia, it's as good a guess as any other.
Of course, if it really
was 3 attempts period, then it
would make sense, but our recollections on that shouldn't be wrong, simply off the fact that he has raised far more than 3 each of previous group mobs, and that even after failing twice or thrice on their respective leaders.