Russian FSB provided Kremlin with false information regarding situation in Ukraine

Before the Russian-Ukrainian war the Federal Security Service (FSB) supplied Kremlin with misleading information regarding the general mood in the Ukrainian society and insisted on a plan to ensure lightning-fast capture of Kyiv, according to The Washington Post.
On Friday, 19 August, The Washington Post continued its series of articles regarding the start of the war in Ukraine and the role Russian FSB played in the development of a plan for a lightning-fast overthrowing of the government in Kyiv and installation of a puppet government.
The Washington Post referenced many representatives of Ukrainian and western intelligence services and wrote that

analysts either misjudged the potential of resistance in Ukraine, or they misjudged it, but they could not or did not want to give Vladimir Putin a realistic outlook.

One of the people interviewed by The Washington Post called the mistakes made by the Russian intelligence «fundamental and strategic».
According to the article, FSB were so confident they would be controlling all reins in Kyiv that the spent the last days before the war setting up informants’ apartments and other locations for the expected expansion of their net of spies.
It was the FSB that clung to erroneous assumptions that insisted on a war plan based on the idea of a lightning-fast assault of Kyiv and overthrowing of the government in a couple of days.
Before the invasion, according to sources of The Washington Post, FSB ordered its informants to leave Kyiv, but keep the keys to their homes.
The representatives of western intelligence services The Washington Post interviewed could not say why FSB believed in the pro-Russian mood in Ukraine, as they definitely had information that proved such a thing is false.
Research & Branding, a social studies company with ties to FSB, reported in a survey carried out in April 2021 that

84% of Ukrainians would consider any invasion from Russian forces an «occupation», and only 2% of residents would call it «liberation».

Nearly half of the country’s citizens (48%), according to the survey, would be ready to defend Ukraine in the event of aggression. Despite this information, FSB continued feeding Kremlin with rose-tinted estimates, according to anonymous sources of The Washington Post.
One such source said «the expectation of being welcomed with flowers came from FSB».

It is unknown if results of this survey were reported to Putin.

«When they started on 24 February, their objective was taking Kyiv. They expected a domino effect that would spread across the country. First they would take the central government, then establish a foothold in regions,» a Ukrainian military source told The Washington Post.
FSB proposed two options for pro-Russian puppet governments. The first would be based in Belarus and would include now ex-President of Ukraine Viktor Yanukovich. The other would include members of Yanukovich’s government and would be formed in Ukraine’s south-east. This group also included former Regional Party member Oleg Tsarev.
According to data from The Washington Post, the main voice that convinced Putin that «Zelenskyy is weak, his government would collapse and that Ukrainians would welcome Russian forces» was the head of Opposition platform – For Life Viktor Medvedchuk, who is considered a close friend of Putin’s and a pro-Russian politician Ukrainian government accuses of treason.