Posterization, sometimes called banding, can be explained by too little information spread too far apart. Have you done all the latest upgrades to LR and PS? One thing you must not do if this posterization shows up is hike up the 'clarity' slider. This makes it worse. Increasing the 'grain' will reduce posterization.
You can also try to increase the color space to AdobeRGB. Some say that doesn't help but it does. Some shots benefit from it some shots don't. The color space in what you see is increased even though the color space outside the ability of your monitor is wasted.
Look at your histogram. It will indicate posterization especially in a processed jpg. The histogram is an invaluable tool.
EB
EOS 1DX and 1D Mk IV and less lenses then before!
