The strongest effect of circular polarizer is at an angle of 90 degrees to the sun. But when shooting with a wide-angle lens the field of view encompasses an area beyond 90 degrees (and less). This can result in uneven exposure and saturation across a blue sky.
When this happens, you can use Lightroom’s masking tool to reduce the visual impact.
Do not get frustrated if you cannot completely remove the dark area, rather aim to reduce the impact of the polarizer.
An alternative techique would be to select a lighter tone Color Range mask intersect with the Sky, darken and increase saturation. This is particularly the approach to take if you intend to darken the entire sky. See the next post.