Final sprint.

I'm playing on Veteran difficulty. I started doing quests after clearing the turquoise area. I encountered a problem. First, there was a message about the appearance of scouts, then about them stealing part of the map. I chased them with four heroes. But in the end, after some time, the mission failed. It's unbelievable – to catch such a huge number of demons that also move around. I think I'm the only one with this problem, which means I'm missing something. I don't see a solution yet.