The Hero's Path

It seems I understand now; you've found my mistake. If you're using mods that add new creatures, the constant for the maximum number of creatures is increased. I force it to the standard value at the start of the map, but due to the order of initialization, it manages to influence the required limit for this achievement.
You can confirm this by looking at:
@print('lim=', achievement_list[14].limit)
It will probably show something like 997.
You can get the deserved achievement using:
@AchievementAdd(14)

By the way, the statistics also show that I lost a few battles, even though the statistics for dead creatures are empty.

Lost, meaning there were losses? Are there no leaders in the number of dead? But are there leaders in the number of killed? Can you take a screenshot? I don't have any ideas yet.