2) When playing through the 3rd mission for Inferno, the heroes' units decrease on their own (i.e., there were 31 archers, and after two turns, there are 30 archers, and so on with all the heroes). Is this a bug or a feature of the game?

That's nothing. Just wait until, in the Necropolis Campaign, after each turn, you lose one or even two dragons. Then you'll start remembering the nuances of the great Russian language! This is perfectly normal gameplay. Everyone who moves around in areas that don't belong to them in the game receives a penalty – a reduction of several units in the hero's army. Later, there will be boots that remove this penalty when in enemy territory.

I noticed an interesting bug in the game the other day. In the 3rd mission of the Necropolis campaign, where you need to capture 3 necromancer artifacts, if you capture the cloak with Isabella and Markel conquers the lower right city and curses it, without giving the cloak to the sorcerer, the mission will not be completed. At the end, when you need to gather 20 bone dragons, the game tells you that you don't have 20 yet, and I already had 78))) Plus, if you curse 3 cities under the same conditions, the game will tell you that you lost!