It seems like every leftist group has their own stance on what happened during the Kronstadt Uprising of 1921 - that it was planned/strongly encouraged by pro-White agents, that it was a mass uprising in the same vein as those in 1917, and so on. Each argument I read invokes sources and perspectives they claim the other sides don't have, and it doesn't help that they all accuse each other of betraying the values of the revolution. In recent years, have historians made headway in trying to find out the full course of events?
The Kronstadt Uprising was predominantly an uprising of sailors, many of whom participated in the October Revolution, when they felt that the Bolsheviks were abusing their power. It was not strongly planned or encouraged by "pro-White agents". The Bolsheviks said that about all dissenting leftist groups (including their temporary allies, the Black Army, who actually fought the White Army).
Despite what anti-revisionist Marxists would tell you, the Bolshevik economic policy of War Communism sucked. A lot of the common people didn't like it (hence why the Green Army and similar peasant rebels existed). A "Third Russian Revolution" nearly happened against the Bolsheviks themselves, and Kronstadt was an example of a anarcho-syndicalist-leaning group of soldiers (led by Stepan Petrichenko, who was an anarchist that left the Bolsheviks, and met with Nestor Makhno) being crushed by the Bolsheviks because they supported actually practicing communism, or an ideology very similar to it, while the Marxists maintained state socialism and eventually degenerated into state capitalism.
Historians, as far as I have seen, haven't made too many discoveries. We don't exactly have a lot of first hand sources that aren't written by the Bolsheviks themselves.