To answer this question, we have to dive into the meaning of the main terms. What does it mean for a country to be communist or socialist?

To start with the term communist: calling a country communist has meant it’s run by a communist party, not that it has implemented communism as a classless, stateless society (which could not exist in the context of distinct nations in the first place, by definition). By this definition, China, Cuba, Laos, North Korea, and Vietnam are communist countries.

PS, anyone saying something like “real communism hasn’t been tried” doesn’t even understand the words they’re using and is not themselves a socialist or communist. Instead, they’re a confused liberal.

Next, socialist, and the idea of a socialist country. There is actually not a shared and specific definition of what would make a country socialist per se, it’s more of a project to deestablish the capitalist class and put the working class in power. Many socialists disagree with one another about whether a given country is socialist, and what is really underlying their thoughts is usually just whether or not they think a country is attempting to deestablish capitalism and/or is making sufficient progress in doing so.

In terms of your specific examples, I’ll offer some critiques.

China, Laos, and Vietnam: now notoriously capitalists. Workers work 12+ hours with no protection in horrible factory conditions. Suicide rates are so high that suicide nets are installed. The air is so polluted millions die from lung cancer, especially factory workers w/out basic masks. Corporations dominate

No socialist expects that the country they operate in after revolution will be free of having to work, for there to be no workplace abuses, for there to be no pollution or healthcare problems, or even for corporations to be immediately deestablished. In reality, what is expected is for the ruling party to begin a long process of undermining capitalist relations. One example is to place human needs into guarantees of the state rather than the whims of private corporations. Another is to quell the anarchy of the market through state controls on production. It is expected that the ruling party will rapidly address the key isy that drove the revolution, which has historically been land reform. An example of this in your list is that every person in Vietnam has a right to an amount of land to farm rice for themselves and their family.

You should also consider that these countries do not operate in a vacuum. Instead, they must fight to survive in a world dominated by extreme international violence, typically from capitalist countries. Therefore, countries like China and Vietnam have adopted specific strategies to deal with this intentional influence, i.e. to combat imperialists. China’s example is one of economic entanglement and to allow private markets in special economic zones, which will allow tons of capitalist elements and social relations to exist there. This strategy is working out relatively well, however: China has advanced concentrated industry and imperialist countries (e.g. the USA) that usually bomb or sanction their way into countries premised on socialist projects cannot do so without devastating themselves. Vietnam was forced into a similar situation but with less leverage and concentration of industry. This is a result of the legacy of being genocidally bombed by the imperialist powers during their struggle for national liberation. They won that war but arguably lost much of the peace, as the imperialist countries, despite stealing so much from Vietnam, saddled them with large debts as a condition for ending the war. Such debts were used to force more capitalist relations, especially foreign ownership, into Vietnam. This is a common story around the world, where most countries are violently bullied into carrying large debts in order to lose control of their own countries’ economies. With all that said, Vietnam is still riledy by a communist party and does distinguish itself from surrounding countries in how it pushes back against capitalist relations and prioritizes its people.

North Korea: Undemocratically ruled by the Kim dynasty. Jong un indulges lavishly at the expense of his citizens, ordering millions in fine wine and trips from Denis Rodman. They might be the most socialist though, as Juche seems to otherwise be democratic.

Nearly all of this is liberal fairytales with little basis. The Kims have high roles in the party but don’t act like dictators, more like figureheads. The primary challenge for North Korea isn’t the Kims at all, it’s the continued occupation of South Korea by the imperialists. Did you know that the Korean War is ongoing and that America won’t let South Korea end it? North Korea is brutally sanctioned at the direction of the United States, and this is where its poverty originates. NK outperformed SK for decades (SK was a military dictatorship at the time) and only ran into famine conditions when the USSR fell and the US imposed an all-encompassing, genocidal sanctions regime.

I don’t think discussing Juche or the NK political system in general would mean anything until the core misunderstandings are dealt with.

Cuba: Sanctions have taken a massive toll, but even taking that into account the country still has its own problems.

Socialism is not when a country has no problems. Socialists are ruthlessly locked in on practicalies, not utopian wishes.

They have massive food shortages and inventory probs and aren’t self sufficient after 60+ years.

This is hardly independent of the sanctions regime and Cuba did not have food security issues for decades until, again, the USSR fell and the US instituted massively broadened sanctions.

Why couldn’t they’ve use machinery imported from the Soviet Union to develop their agriculture and fishery?

They did. Who told you they didn’t?

The Soviets supported them heavily.

The Soviets traded with them when the imperialist powers were brutally sanctioning them. Cuba was not a client state being provided with alms. It was a recently decolonized country that had just survived a revolution and needed to build in the context of being treated like one big sugar plantation, brothel, and casino for Americans. They had to develop industry from the ground up and they routinely outperform the richest country in the world on health metrics, their healthcare system, and healthcare research.

They seem to be incredibly mismanaged or corrupt

According to who?