Why? It sounds like you're using "I believe it's rapidly getting smarter" as evidence for "so it's getting smarter in ways we don't understand", but I'd expect the causality to go the other way around.
The more complicated and/or complex things become, the less likely it is that a human can act as a reliable judge. At some point no human can.
So while it could definitely be the case that AI progress is slowing down (AI labs seem to not think so, but alas), what is absolutely certain is that our ability to appreciate any such progress is diminishing already, because we know that this is generally true.
Give me an example, please. I can't come up with something that started simple and became too complex for humans to "judge". I am quite curious.