When your vassals get attacked by peasants and they win (which happens all the time in China) they then become escalated peasant factions and a problem for you. This system, while interesting creates factions that are almost unbeatable. While I do enjoy challenge these factions are nigh impossible to beat by their sheer volume of troupes and how spread out they are.
For example in my 867 Tang game I had in my second year a faction of about 10K peasant. Nothing thats unbeatable for the Tang dynasty and then one year later I had another escalated faction with about 24K still nothing too serious. But after that year I had again ANOTHER escalated peasant faction with around 40K peasant all over China(I have about 10K soldiers) and since I played in 867 they could take a fort in about 10 month making it so they would win in the same amount of time.
I think I'm pretty good at the game with my 5K hours but I genuinely think its impossible to win without exploiting the game. I'm not sure if this was the intended goal of Paradox with escalated rebellions but in any case its not a good system and it would need a rework because now it results in a very frustrating situation where, as the emperor of China, I can do nothing but see my empire being torn apart by rebels that I have beaten again and again.
I guess you could micro-manage every single vassal of China to check if any of them is getting their ass kicked by rebels, but I don't think its a good system if its indeed the intended solution and realistically you can't participate in 10 wars at the same time all across China.
Now, what could be the solution to this? Well, I don't have much of an answer but maybe you could put a hard stop for escalated peasant factions for about 10yrs or put all the rebels in one spot so they can't siege the whole of China so fast but even then that's just delaying the problem. It's a very frustrating issue and I really hope someone can fix it because China(867) is unplayable.