Zones of control are still an awful mess. The mechanic should never have made it out of alpha in its current state.
(1) First, it turns forts into special snowflake buildings that, unlike every other building in the game, fundamentally change neighboring provinces. This is bad design because it creates a special case that violates player expectations and needlessly increases complexity.
(2) Second, figuring out what forts a player must siege involves too many special cases. In theory, forts control neighboring provinces. Unless they're allied/vassal forts or provinces, in which case the zone of control does not span borders. Unless the player demands a province, in which case the game looks to the nearest fort of the province's owner. Unless the fort is mothballed. Unless there's an occupied province between the fort and the target province. In short, there are too many bloody special cases involving zones of control.
(3) Third, army movement routinely breaks in any situation involving multiple countries or wars. Armies routinely forget where they came from and are unable to exit enemy provinces. Armies can take paths deep into enemy territory, then decide that they can't take that same path back even if nothing else has changed/ Armies cannot embark on transports from which they came after landing in enemy provinces. Some armies cannot follow paths that other armies follow, probably due to conflicting permissions/prohibitions on movement, such as wars within/against HRE and non-HRE members.
(4) Fourth, information on zones of control and forts is buried in a special map layer. Forts are difficult to see on the map without using a special map mode, which means the player must constantly flip between maps to find essential information such as zones of control, terrain, and country borders. This is bad design
In short, zones of control violate fundamental design principles, violate player expectations, and behave in a way that possibly makes sense to the developer but appears to be utterly psychotic to an outside observer.
Edit:
Examples of counterintuitive fort behavior in my current England game.:
England (player) is at war with France.There are forts at Paris and Poitou.
My army in Vermandois can cross through Paris (fort) to go to Orlannais, even though forts are supposed to act as roadblocks. I can only guess that this is because I control provinces on either side of Paris and perhaps should always be able to enter provinces I control.
This army in Anjou cannot cross through Orleannais to go to Nemour. Nor will it be able to cross from Nemour to Orleannais when it eventually arrives. Presumably this is because of the Paris fort's Zone of Control acting as a magical roadblock to divide the two provinces even though it is under siege and I have control of or access to provinces on either side.
But note that once I siege down Nemour, I will be able to move through that chain of provinces at will.
This army cannot go from Berry to Lismousin next door, even though I control Berry. But it can freely wander across Bourbon and into Lismousin even though I do not control either of those provinces. Because apparently it's more difficult to go across the French countryside where I don't have troops than where I do just because there are fortifications a few hundred miles away.
I should probably note at this time that the AI has no idea how to plan around zones of control. In the above game, Austria got eaten alive by France because its armies wound up on opposite sides of a fort's zone of control and could not reinforce one another. In one of the links, the Austria AI decides to engage a numerically superior French stack, presumably because I have two large stacks next door. But I cannot move to reinforce Austria due to zone of control.