I can’t get the super ability.

Hello everyone!
We're playing with a friend in Heroes of Might and Magic 5: "Tribes of the East" 3.1 - a non-licensed version.
We're playing through Hamachi, with random maps, different difficulty levels, and different factions.

So, the problem is that, following the skill tree towards the Archmage specialization, at some point, the required skill isn't offered. That is, the right side is empty when leveling up, and the left side offers unnecessary skills.

Moreover, I clearly remember that the necessary skills were offered at previous levels, but I chose something else (also useful). It feels like after you "refuse" a skill several times, it's no longer offered.

I'm already very frustrated.
Can anyone tell me what's going on?