Not a mystery at all, unless you start with the premise of the "Human Exceptionalism" and as jolux rightfully points here, the publisher Discovery Institute has even a whole department called "the Center on Human Exceptionalism."

That's how they start from the false premise and come to the false confirmation of that false premise with a religious answer that it's "a mystery."

Interestingly, the editor of this particular publication writes in his article that he is aware that one doesn't have to start from such a false premise, but that they go "way beyond this":

https://mindmatters.ai/2018/07/why-mind-matters-matters/

"Consciousness, for example, is defined in the dictionary as being aware of your surroundings. A robot with environmental sensors is conscious by this definition. In our discussions, the topic of AI consciousness is way beyond this."

At least he doesn't use in that text the direct "it's a mystery" approach. But looking at the titles of the articles there where he's an editor we see:

"Possible Minds?: But What If the Minds Are Impossible?"

"New Evangelical Statement on AI is Balanced and Well-Informed "

"Why Apes Are Not Spiritual Beings"

"Things Exist That Are Unknowable"

Etc.