Chromatic aberration is an extremely common lens problem that can leave your images with weirdly colored edges. In its more subtle incarnations, it can be easy to miss until you've already exported the image, but it turns out Lightroom has some helpful tools to help you see where it might be hiding.
Chromatic aberration is a type of aberration that is caused by lenses having different refractive indices (the ratio of the speed of light in a vacuum versus that material and a measure of how much said material bends the light) for different wavelengths of light. The result is that varying wavelengths are bent by varying amounts, causing the lens to be unable to focus all colors to the same point. The unfortunate consequence is that your images contain green or purple (typically) bands around high-contrast edges. However, when you're check for its presence in an image, it can be difficult, as it is often only a few pixels wide, and in a complicated image with millions of pixels, you might not see it at first. This helpful video from Anthony Morganti shows you some of Lightroom's hidden built-in tools for tracking it down and correcting it. It's a quick and effective way to improve your final output.