I am playing the latest GoG reforced version and I have reached Aonir's blade in the campaign where I am supposed to break down the gates of the fortress using the falcons' catapult.
But there is no way to load it, no load option even appears at all, only the fire option - which does nothing since it's not loaded. I was expecting to see an option for load next to the fire command in the box bottom right, but nothing.
Is this a bug in this version of the game or am I missing something here?
I attach an image of my screen showing the catapult command.

Note, I have run a file verify on the game through gog galaxy. I tried restarting this zone with different armies, and taking different choices, but this is always the same, no load button appears and I can't progress.

As far as I remember it must be loaded with stones, some workers must be assigned to it to deliver them.
Also all the areas arount it must be conquered first.