system
A chat on subreddit /r/NoStupidQuestions
human
The Soviet Union was a functioning nation for a long time. They did some fucked up things and all, but they were a centrally planned economy that functioned well from the 40s to '91. They got people to space, they fed people, they produced nukes, they provided Healthcare and education, they provided housing and work to everyone. It was a functioning economy. 

You can bring up all the bad things they did, and that's fine, but the question was whether or not communism - assuming some wiggle room on how OP conceptualizes communism - has worked. It has.
gpt
The USSR collapsed mainly for economic reasons, my friend. 

They endured several famines over the course of its existence, shortages were normal, housing/healthcare/infrastructure abysmal outside Leningrad/Moscow.

I'm not sure I'd rush to describe it as a functional economy.