There were numerous struggles and issues with the USSR, of course. There was corruption, especially among the Politburo. The focus on heavy industry over light industry, though favorable during WWII, resulted in fewer luxury commodities, which resulted in liberalization and collapse.
Fundamentally, it is entirely silly to say that the USSR wasn’t leftist. It absolutely was, even if it was highly flawed and imperfect. In fact, it’s useful to analyze what went right (free eduaction, high home ownership, generous social safety net) and what went wrong (corruption, lack of luxury commodities, etc.) so as to come up with a better system.
That is, unless you think Marxism isn’t leftist, and think only Anarchism counts as leftist, in which case I really don’t know what to tell you.