Every estate has one of these events that add 10 or less likely 20 influence (determined before you click the button so the tooltip will tell you how much). They can't retrigger until the effect from the event wears off. There is also a companion event that reduces influence without you doing anything that follows the same rules.
The problem here is that the existence of these events simply ruins the entire system because there's always the threat of +20 influence hanging over your head. It means you can never use any combination of actions for your estates that raise their influence above 59 (Which is most of them -- min 50 + 15 influence from clicking the action = 65 influence minimum for using it). The only recourse is then to start revoking estates, which VERY quickly lowers loyalty, giving you the /opposite/ side of the spectrum with even more bad events (-2 stab and peasant rebels in every owned (???? by the estate? I clicked the button and got no rebels even though it said spawn rebels "in every owned province") province, to name one) and passives. So then the only way to /raise/ loyalty at that point is to pay ludicrous amounts of resources (100ish ducats for +10! Really!? I didn't even have 30 ducats in the bank!) or to give the estates more land... but oops, can't do that because they're already at too much influence.
If those events also raised/lowered loyalty respectively (raise with adding influence, lowered with subtracting influence), then they'd be /okay/. But as it is the only thing they do is screw you at inopportune times. Because while they may not be that common, you have to always expect them to happen, in a 'everything that can go wrong, will go wrong' kind of way.
Actually you can see that there are estates on the land of other countries. I've been going over the provinces of my allies and marveling at how many estates they have. Not sure if I can see that ONLY because they are allies though. Either way this just makes us more cautious about large land grabs and makes eating our neighbors more difficult. Having to wrestle with elements from our own government for control and constantly balancing those conflicting forces....and integrating new lands....just seems more realistic to me.
You can see that they exist on that land, but there's no indication anywhere as to how it would affect your nation if you conquered those provinces. Sure, that province has nobles. But how will that affect /my/ estates? In fact, where's the indication in the peace screen showing what the estates on these provinces are? Sure, I can leave the peace screen and check them, but only if I know beforehand that they get carried over, and it assumes they don't do something silly between the last time I checked like say, add a whole bunch of the same estate to those provinces right before they accept the peacedeal (since it seems like you can assign estates at any time, even if a province is occupied? Works with rebel occupation, for sure. Not sure on nation occupation, but afaik rebel and nation occupation are treated the same way.)