Sierra broke display on headless Mini Server
I upgrade my headless Mac Mini (4,1) to Sierra and updated Server to 5.2. Since doing so, when I try to Share Screen, all I get is a black window. IF I plug in a monitor to the Mini, then Share Screen works. I can then disconnect the monitor and everything stays the same until I reboot. Once I've rebooted, I get the black screen again when trying to control remotely. Remote Management is turned on in Sharing Prefs and Observe & Control boxes are both checked. All other services are working fine.
Everything worked just fine with El Capitan, it was only after the upgrade to Sierra that this behavior started.