There were several, but the Hamilton 68 hoax is one where censors claimed many accounts were Russian bots but were actually mostly American. Twitter found a relatively small amount of the identified accounts to be actually tied to Russia. https://search.brave.com/search?q=hamilton+68+hoax

Many people probably only remember all the news from MSM about the Russian bots but never saw this reveal that it was a hoax as it was not reported much in the MSM.