After I upgraded an MBPr to 10.12 Sierra, the 4k external display connected to it shows significantly less options under Display > Resolution > Scaled (pressing Option to see the resolutions). Before, I always used it at resolutions between 2160p and 1080p, generally 1440p, but those are gone now.
What could cause this? How would you troubleshoot it? I'd rather fix it without having to force the resolution in configuration files (like I had to do years ago), but that'd be better than this situation.
I purchase a new MacPro (the little black trash can) and shortly after, chose to install the Sierra update. Upon restart, it would not recognize my Apple Cinema's high res settings. After 3 hours with Apple tech support, they filed a report to Apple engineering who solved my problem with this solution: