Series authors sometimes get bored with their characters and decide to retire some of them and introduce replacements. Fourteen books into her Sano Ichiro series, I think Laura Joh Rowland has reached that point. Sano's fortunes have risen and fallen since he was plucked from the police force to serve Tokugawa Tsunayoshi, but The Cloud Pavilion feels like it's signaling a wider transition.
A few years ago, I declared "the year of the subplot" - a comment on the number of (often poorly integrated) subplots the mystery series authors I read fell compelled to include. Perhaps it was because their publishers required manuscripts of a certain length, but most of those novels would have benefited from either excising the subplot or adding 30 pages to better integrate them into the story. In The Cloud Pavilion, Laura Joh Rowland gets it right.