MacOS 10.12.X Video resolution issue
External monitors in 10.12 issues.
I know I’m not the only one to discover this bug but thought I would document what I have seen.
Machines that were running prior versions of MacOS and were previously connected to specific models of external display will “cache” or learn the display settings. So when they upgrade to 10.12 they won’t see the issue for displays they have already connected to but if they connect to different displays they will not be offered optimal display options. An example today was for a monitor that could do 2K but was only being offered 1280×800.
This issue is worse in the new MacBook Pro laptops because they can’t be run on 10.11. So almost any external display will not run at the optimal resolution. I have confirmed this with a couple of HP monitors and an LG. Even when you do use Migration Assistant from a machine that has used external display before that “cache” or whatever is not carried over in the migration.
I am assuming that if you target boot the new device or image the machine with an exact copy of 10.12 the monitor “cache” will follow and it should work. I will test and update the post.