Well… There was this thing called Soviet Union. They decided to try to speed up the transition to communism by using repression and violence. And ended up being a totalitarian state, a direct opposite of what a communist state is supposed to be like.
Of course you can argue that Soviet Union was not communist, it was just a state that had chosen to call itself communist for propaganda reasons… But still, Soviet Union is an example of a communist country that was unsuccessful as a communist project already by itself. Then came outsiders and helped make it even worse, but bad doesn’t become good by some people wanting it to be even worse. Burma is another example. I’d say they hacked away their own leg before anyone else, such as CIA, had time to interfere in their business.
Finland decreased its poverty between 1917 and 1991 more than Soviet Union did. In the beginning of year 1917 Finland was a part of the Russian Empire, so we were extremely poor here as well. Soviet Union could be on the second place, perhaps. But, since there is at least one country that fared better, the claim you made it evidently false. There can very well be other countries than just Finland that decreased poverty more than USSR did. I do not know for sure, though, as I’m not terribly well aware of how faraway places like Chile or Burma were faring in 1917.