I don't know if its intensional or a bug, but the extra fight you trigger with the blue summoning circle in the missions that unlock once you hit level 78 (starting with finding the detection powder mission) the enemies in that fight are at least ten levels above 88, 90, etc making these fights much harder than the ones from previous missions as those were always the same level or one/two higher.
Its strange that the level gap jumps to much all of a sudden when compared to previous missions.