The dissatisfaction and impeachment received by the Demon Cleansing Bureau are partly because Han Zheng killed Sheng Tian'an, and the network of contacts left by the Duke An Mansion is at play.
The other part is due to some nobles being dissatisfied with how abruptly the Demon Cleansing Bureau has taken action against the underground forces in the Capital City.
The underground forces in the Capital City are not merely underground forces; almost every faction has a noble as their backer.
Without a noble backing them, most would be exterminated within a few days.
It can be said that these people are essentially the dogs kept by the nobles in the Capital City, doing dirty work for them.
The Black Feather Building has become the leader of the underground forces because Sheng Tian'an, despite losing his title, is still one of the nobles.
Now, with the Black Feather Building being swiftly wiped out by the Demon Cleansing Bureau, other noble forces are somewhat fearful.