I can't figure out if this is something I'm doing wrong or if it's a technical issue.

I've just started playing this game and am having trouble at The Siege stage. I seem to have killed, recruited or chased off all of the neutral units across the map. Everything said it was neutral, though there were pauses for 'Red Players Turn' I never saw anything owned by the Red Player. I've built and upgraded my Jousting Arena and that objective has been checked off. I can't seem to get the game to check off my 'Clear the Area of Enemy Scouts' objective. Am I missing something? Could this be a bug? I've seen the celestialheavens map of this scenario and have triple-checked all of the spots there were supposed to be enemy scouts. I've even gone back and started the scenario at an early save point in case it was a problem that last time I killed everything before building my arena, but it didn't make a difference.
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I'm having the same problem. It's really frustrating.

Go to the part where the map is grey (not black) and go further.
The enemy hero will be there.
He will come to you if he is in visual range.