We've been having this issue for some time... and looking through the forums I see that people have been complaining about this problem as far back as CS6. I should also add that the people commenting in the past have been on both Macs and Windows. So this looks to be an engine problem not a platform-specific issue.
Before you comment, let me ensure you this isn't a color bit-depth setting problem within Premiere itself... this is purely an issue introduced when exporting video out of Premiere regardless of the output files target bit depth.
I can confirm this is STILL an issue under Adobe Premiere CC 2017.
I've also seen subtle color shifting occur when exporting out of Premiere. But I digress back to the original topic.
To preface I should state that each of our guys tasked on attempting to solve this problem in the studio have well over two decades of post-production technical experience.
Source media in the Premiere timeline are ProRes4444 (also tried ProRes422HQ).
Viewing them in Premiere they look perfect. However, the exported file has significant banding introduced into the output file.
We have tried exporting in every single ProRes format available... without any difference in the introduced banding.
We've tried every thing possible we could think of:
1) Setting sequence to maximum color depth
2) Setting sequence to maximum render quality
3) Setting export to maximum quality
4) Disabling metadata at the export
5) Exporting to various tile types and bit depths.
Nothing changes the output.
We've attempted exporting an animation codec version which also has the banding, but barely reduced overall.
HOWEVER... if you IMPORT this project into After Effects and render the timeline from within After Effects.... there isn't any banding at all. So clearly there is a major issue within the export engine that Premiere uses. Our only work around to ensure there isn't banding, as well as not having the color shift I briefly mentioned, is to import the timeline into After Effects and rendering from there.
This is a significant flaw in Premiere that is just mind-boggling that it has existed for at least 4 years at the minimum. Adobe should be putting this problem at the top of their bug fix list for Premiere.
Let me reiterate that our exports from Premiere were set to Maximum bit depth and maximum render quality. And we rendered to ProRes4444 files.... the same format in which the files were sourced... but banding was introduced.