For the most part, the fault doesn't lie with the adventure writers. They use the CRB encounter budget guidelines correctly.
There are a few cases of overpowered critters. The
Corrupted Retainers are listed as level 2, but have been shown to more resemble strong level 3 creatures.
Mistress Dusklight's circus bouncers are probably within the range for a level 8 creature, but it still feels off that a creature described as a "bruiser" should have elite fighting abilities. In my mind a "bruiser" is more like a "brute" than a "soldier" to use 4E terminology, so I've lowered their attack bonus by 4.
For the most part, anytime the party can heal up after an encounter, they will be fine, no matter what the next encounter holds. And the adventure very rarely makes this (getting 20-60 minutes of undisturbed downtime) difficult. But the very first chapter will probably go down in a single evening. It's possible if not probable they will have to fight the end boss with every resource already depleted, which a GM should be aware off beforehand. (It can easily take a GM by surprise, given that it's the first level of perhaps your first PF2 campaign. Yes, I'm talking about myself
)
The very end of Chapter 8 doesn't read as being different, but if you look carefully at the map and
Mistress Dusklight's abilities, you'll realize she can send heroes back into the maze, making the fight against her potentially life-threatening for the heroes that remain. Again, the problem is the potential for taking a GM by surprise.
On the other hand, some supposedly difficult fights, and indeed entire chapters, play much easier than they read. Part of this is the timing of the martials' striking runes (if players sink all their money into getting them as early as possible that will likely make that level clearly easier), part of it is how certain levels represent a much bigger upgrade than others. And of course part of it is the nature of the monsters - a given party will obviously be better geared to handle some types of monsters than others. In a few cases the difficulty could even be ascribed to me misinterpreting a given monster's ability or tactics: it took me a while before I realized a monster needs to spend an action to maintain a Grapple, and I probably ran the
Smoldering Leopards and the
Vrock wrong.
Our group found levels 1, 3 and 6 to be especially difficult. On the other hand, level 4 was rather easy and level 5 would have been easy had I not attempted to slow them down by upping the monster challenge (as I'm sure I've explained upthread).