The long gap between seasons was enough to get excitement for Curb returning, but it was also helped for me by how good the previous season had been. In essence this season looked like it would had a great through-line with the fatwa and the related musical (albeit a bit similar to a previous season). It doesn't run through this very evenly, but mostly it does the job, while the random misunderstandings or poor social interactions do the rest of the work. It is frequently funny, but never as consistent as I would have liked. There are callbacks and repeated elements, which add to the impact of the lines, but again - not enough.
The most obvious place to see this not working is in the ending. At its best the final punchline is the strongest callback - it ties the episode up in an absurd bow by linking back to what had gone before and doing so in a way that makes you groan by how obvious it is (in retrospect) but yet be inspired by how smartly it all clicks. There isn't really a single episode that pulls that off here; okay they all reference something from the episode but they are not really strong or punchlines. The show still does its base elements well, and it is hard not to enjoy it for David's brand of humor, but it doesn't click and spark consistently, even if it produces plenty of moments along the way.