Sanctuary – “Life in death and death in life” [Campaign 4 – Mission 4]

Guys, please help. I'm playing on normal difficulty. I'm getting reinforcements on the island in the upper right corner of the map and leveling up quickly... But it's no use... What you're all talking about – demons and humans destroying the enemy's legions – isn't happening for me... Maybe it's a bug...? The threat level is always deadly... Once, I defeated the demon lord, and then a warlock of level 25 appeared with an inexhaustible army... Where are they getting it from? Is this mission about speed or about waiting? I can't wait – their army is growing exponentially... My people are weak and are hiding in the castle... How can I complete this damn mission? For me, it's the most difficult one...