Display resolution options disappeared after upgrade to Sierra
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:


Shut down your machine
Unplug all of your monitor's connections (in my case, 2 USB and 1 Thunderbolt) and reconnect using only the ports on the RIGHT side of the Mac.
Voila! They said they are aware of the glitch, are attempting to fix it, and until now, this should work.