There have been examples of anarchy working. Unfortunately, most of the ones I know of were around during World War 2 and got crushed between 2 larger opponents, or backstabbed by one of them.

• Anarchists - and other socialists in Catalonia - during the Spanish Civil War, were stuck between the fascists and the republicans (Soviets), sided with the Soviets and ended up being betrayed. Homage to Catalonia by Orwell is a good book about the civil war and the anarchists.

• Korean People's Association in Manchuria were destroyed by Japan a few years before WW2 during a war between China and Japan IIRC, and apparently some of its leaders were also killed by "Korean communists" (the same ones that ended up forming North Korea).

• The Black Army of Ukraine fought the Red and White armies at separate times; one time they joined the Red Army against the White Army, and were betrayed.

You might have noticed a pattern there, which is also why a lot of anarchists are not found of Marxist-Leninists or Stalinists.