The argument from ignorance

Atheists often mock the Christian appeal to mystery or paradox. They think that's intellectually evasive. A cop-out.

Before getting to the main point, I'd note that mystery and paradox are not synonymous. A logical paradox is mysterious, but a mystery isn't necessarily paradoxical. 

On a related note, atheists accuse Christians of resorting to an argument from ignorance or God-of-the gaps. However, in other contexts, atheists appeal to mystery. For instance, some atheists say we may never be able to explain the naturalistic origin of life because we don't have enough physical evidence about primordial conditions to reconstruct the distant past in that regard. In principle, we could explain the origin of life naturalistically if we had enough trace evidence to reconstruct the initial conditions, but that may be lost. 

More dramatically, some atheists say we find quantum mechanics baffling because our simian brains were not evolved to understand that sort of thing. That kind of intelligence didn't confer a survival advantage on the ancient African savannas for our early ancestors. So natural selection didn't develop brains that have the cognitive ability to resolve quantum mechanical paradoxes. In that event, it's something we can't figure out even in principle. Human reason is too limited. It hits a ceiling.

Likewise, there may be problems in math that are humanly insoluble. Once again, our simian brains evolved to solve more practical problems. So we hit a wall.