I had an issue with adding shadows to labels and having them disappear on iOS 10 only (worked fine on anything lower).
It's caused by the size of the dimensions you give the label. I found iOS 10 you need to give a lot of extra space to not have labels just disappear.
When you create your label, add a lot of spare room in the dimensions and use:
Label.horizontalAlignment = CCTextAlignmentCenter; // can also set to left or right
Label.verticalAlignment = CCVerticalTextAlignmentCenter; // can also be set to top or bottom
and anchor points to position your label perfectly no matter what size your label dimensions is.
For my issue, let's say my font size was 10 and my Y dimension was 15, it still would not render. I had to make at least double my font size to be safe.