I do not think it indicates an unfixable problem with the ideal. It does indicate fatal flaws with the plans to get there. That is why I believe we need better theory on how the communist ideal can be achieved in a democratic way. I do not know if this better theory can be developed. And I do not know if humanity will ever align with this ideal. The communist ideal of a classless society is in many ways unnatural and presupposes that we will overcome some of our vices. Note that this does not solve all of our problems and therefore I think it is outdated. The 17 UN SDGs are a far more up to date set of directions we need to work on.

Just to make it clear, I think the 10 planks/10 point action plan of communism from the actual manifesto is simply WRONG and would never have achieved the communist ideal (and nowadays it is also outdated). An authoritarian nightmare is the direct result of that plan, points 1, 3, 4, 8 and 9 ensure that. Even more damning and depressing is that many communist regimes did not actually implement point 10 by actually having mandatory child labour even if education was free.

But also note that most capitalist countries actually implement to some degree point 5 (having a national central bank) and many to various degrees implement point 10 (free education, no child labour) and several implement 6 (state controlled transportation and communication). And this was for the better.