The issue you're referring to is similar to what János Kornai, a Hungarian economist from the communist era, referred to as the "shortage economy". He wrote an entire book about this phenomenon, but the tl;dr version is that command economies simply aren't built to respond to the shifts in supply and demand of consumer products because they don't react naturally to those changes in the way that a market economy would.

Since the amount of a good produced and the price of that good are centrally controlled, you can have adequate supply of a product and still end up with a shortage because the demand for that product outstrips the demand at that particular price (i.e. people buy more of the good because it's cheaper inducing a shortage). Often, by the time the central planners responded to the shift in demand, either by producing more of that good or altering the price, the demand was no longer present, so you went from having a shortage of the good to a surplus of it.

This cycle of shortage and surplus has effects on the consumer beyond simply not being able to get a product that they want. They may have to resort to what Kornai called "forced substitution", i.e. buying a product that isn't really what they wanted because it's the closest available thing to the product they wanted. If there isn't a substitute available, they may end up with "forced savings", where they don't spend that money at all. Because the planned economy doesn't correct itself for these problems, the planners are essentially playing a game of whack-a-mole, trying to either react to existing shortages or predict where consumer demand will go next, which is hard to do under any circumstances.

Kornai was primarily writing about Hungary under János Kádár, but the shortage economy was common throughout the Eastern Bloc, and other countries (including Poland and Romania) went through the same sort of economic stagnation that Hungary did in the 1970s and 1980s; in fact, most countries were worse off, since Hungary was generally considered to have one of the higher standards of living in the Eastern Bloc during that time. The efforts of the politicians to resolve these issues and provide more and better quality consumer goods, such as the economic reforms in Poland under Edward Gierek in the 1970s, were ultimately undermined due to the systemic shortcomings that Kornai identified.

Of course, there were cases where the issues went beyond the structural shortcomings of communist economics and were instead the direct result of policy choices by the countries' leaders. Romania is a good example of this. The Romanian economy had already experienced stagnation in the late 1970s, accompanied by a large increase in the national debt. In the 1980s, Ceaușescu decided that Romania should pay down its entire national debt (about $10 billion as of 1981) by the end of the decade through a crash program of fiscal austerity. As a result, for most of the 1980s, Romania exported large amounts of food, oil, and other products, while Romanians endured severe shortages and strict rationing of even the most basic goods. Romania did pay down its entire debt by 1988, but by that point, a decade of suffering due to Ceaușescu's austerity policies had already sown the seeds of the communist regime's demise. I realize that wasn't really what you were asking about, but I thought it was helpful to note that there were both structural and policy issues that caused the Eastern Bloc command economies to struggle in distributing consumer goods in an adequate manner.

Source:

Kornai's book, Economics of Shortage (North Holland, 1980), is worth reading if you're interested in a deep dive on postwar communist economics, but it's pretty dense.

Most resources were allocated towards “strategic” production - defense and heavy industries - which were seen as critical for country’s survival.

Then there was the very real and very serious problem with the lack of housing. Trying to solve that used up much of the funding left over from the “real” industry.

The consumer goods were almost an afterthought and the amount of resources allocated to their production was insufficient.

Also the 5-year plans greatly emphasized quantity over quality. If you were a plant manager, the expectation was that you would not just meet but exceed the (already unrealistic) plan targets. Any real QA would just get in the way of numbers. Basically when it came to consumer goods, poor quality got you a slap on the wrist, not meeting quantity targets got you demoted. Poor quality but exceeding targets = praise and bonuses. In really simple terms, quality is not an easily quantifiable metric, and can’t be used to effectively measure performance according to the Plan. And exceeding Plan targets benefited everyone from the lowly worker to the Party secretary responsible for your plant.

Finally there was very little that the plant management could do to punish the workers who continually failed to meet quality standards. They could not be fired, their base salary could not be slashed, and if they met the plan, they expected bonuses.

In short, the entire system was not conducive to quality.