Humans have limited "working memory". We manage to cram more into it via hierarchical decomposition into "chunks", a single concept that is more complex inside.

I submit that not everything can be hierarchically decomposed in a way that's useful - i.e. any "abstraction" you try to force on it is more leaky than non-leaky; in that it doesn't simplify its interactions with other chunks. You might say it's the wrong abstraction - but there's no guarantee there is a right abstraction. Some things are just complex. (This is hypothetical, since I don't think we can conceive of any concepts we can't understand.)

An AI could have an arbitrarily large working memory.

Note: I'm talking about intuitive understanding. We could use it mechanically, just never "get it", cowering before icons, being the one in Searle's Chinese Room https://wikipedia.org/wiki/Chinese_room