"Flight to Salvation" - "The Veil is Torn" [Campaign 4, Mission 2]

Perhaps it’s a bug, but after attaching a garrison and building a Knight Castle in the south, it became impossible to convert white units into red ones. Also, the battle with the demon at the end is difficult because the imps steal 120 mana from Freya immediately, and she essentially relies on free spells like Prayer, Reinforcement, and Inspiration. Almost all units are killed, except for the Adepts and Zealots.