It’s saying that 16% of the problems have well, problems.

You're right - I did not apply the math. (I won't edit, in order to let the parent comment still make sense, and thankyou for the correction.)

So not one in four, but one in six problems have problems.

That is extraordinarily high and the point still stands: is this truly saying a [large proportion] of the questions and answers were wrong, this whole time, and if so how was it ever a valid measurement?