Maybe we're using different words for the same thing. But I've found that when I get "stuck" like that, it's because I'm trying to fit too much into my working memory, and I start losing track of it and am unable to recall parts of it, leading to confusion.

So I do what you say, except it's much more deliberate than just "slow down" and "re-read". I try to break the concepts down into chunks, and focus on being able to recall specific things about each chunk. First I convince myself that each chunk makes sense in isolation, and then what its "contract" is (how it interacts with related concepts and fits into the bigger picture). When I can easily recall both of those in a coherent way, I'm ready to move on. I use a variety of ways to practice recall, depending on whatever's most ergonomic (Anki, study sheet, deliberate practice, etc.). Sometimes I find that I lack enough understanding of other concepts to really understand a chunk, so I have to go recursively do the same thing for other concepts.

So I see it as more of a memory problem and not "understanding". I don't really know what "understanding" means, to me it's all just memory--memorizing why something is true/makes sense (by relating it to stuff I already know/memorized), and then memorizing how that thing fits into other contexts. If I can't load that stuff quickly into my working memory, then I don't "understand" it.