How does AI create troops out of thin air?

[YerCo]

I came back to the game after a long break and found a very strange thing that was not there before - the AI started to create troops out of thin air. These troops are in the "Special Soldiers" category and can be of two types: "Mercenaries" (consisting of Levies) and "Someone's Host" (for example, "Duke Otto's Host", usually consists of Armored Footmen). And these "Mercenaries" are not ordinary mercenaries. They, as I say, are "Special Soldiers", appear instantly, do not require money to hire or maintain, their contract is perpetual and they are inherited.

Duke Richard has ordinary mercenaries ("Company of Bretons") whom he hired for money and these strange "Mercenaries" (which are special soldiers) whom he made for himself for nothing.

Duchess Irene just made herself two squadrons of heavy infantry without paying a cent for it.

How does the AI do this? Is there some decision or event? What am I missing?

 

[Benismann]

There're a couple of events that give special troops. Idk which one gives HI, but it's def not some new one, and "mercenaries" come from a generic travel event where you can pay like 60 gold for 1000 levies as special soldiers OR recruit a giant (idk if they're guaranteed to be giant) character with good prowess OR just pass by

 

[DiabloDeVille]

I'd guess mercs are from the travel event where you pay too much money for more levies. The host with actual MaA might be from a civil war event that gives you troops, or a hostage's family giving you troops instead of joining the war. Theres a further thin air creation whenever you first grant a county to someone, theyre meant to get MaA, this is also meant to happen at game start so the player cant snipe at easily