As an active researcher, I'm not surprised at all. It's common enough that people in the same field but a different subfield cannot properly understand a publis

As an active researcher, I'm not surprised at all. It's common enough that people in the same field but a different subfield cannot properly understand a published paper. The same is often true for people working in the same subfield but on different topics. Just read all the horror stories about Reviewer 2. With some scientific literacy, you may be able to understand the central claims made in a paper. Or you may misunderstand them, because you may not be aware of the specific meanings of some words that are also used in everyday language. You may not be familiar with the context the paper was written in or with the best practices in the field. Hence you may not see the implicit assumptions that were made or know the justifications for certain choices. Because you are not an expert in the topic, you may not see the immediate consequences of the claims and are likely to take them too literally. It doesn't help that the authors probably didn't understand the results fully either. Most papers are difficult to understand, because they discuss early insights rather than final results. Clarity often comes with a better understanding years after the initial publication.