Probably this will be an outdated post now, but the problem is with the mod Maps_ToE_UnlockAllHeroes.h5u, which unlocks all heroes available in the original game for recruitment. Delete it, and the problem will be solved (mission 4 also doesn't work because of this mod). Gold Edition? That's a pirated version packed with old mods, like minotaurs without helmets, beta ents, and dark elf riders. It would be better to download a clean version.
Thank you! It helped. But the downside is that you'll have to replay the mission because the changes don't work on a saved game.
