macOS High Sierra: Mirror issues
High Sierra “Known Issue” with DisplayLink
There is one new key issue to call attention to, which is a bug in macOS High Sierra that prevents ‘mirroring’ displays with a DisplayLink adapter. Attempting to mirror a virtual display will cause the Window Server to crash and logs the user out, so it’s an unpleasant bug which we hope will be fixed in an upcoming High Sierra patch. To increase its priority, DisplayLink recommends reporting the bug to Apple.
DisplayLink’s own bug is tracked under ID 33650324. Apple’s internal defect number for this issue is ID 26394372.
DisplayLink has additional detail about the issue in their knowledge base. It also speaks to instances where the OS will default to mirroring when a display is plugged in (rather then extending) causing a frustrating crash due to the bug mentioned above. DisplayLink has a utility available that can reset the layout persistence settings in the OS that can help workaround this behavior.
http://support.displaylink.com/knowledgebase/articles/1812676-macos-high-sierra-mirror-issues
When the display layout is set to mirror, the Window Server will crash terminating all open applications. The layout will be reset to extended screens and the user brought to the login screen.
In some cases it's then possible to mirror after logging in, but subsequent device unplugs can trigger further crashes.
This issue is particularly severe in configurations that default to mirror. In these cases simply connecting a monitor or rotating a screen can trigger the Window Server crash.
The operating system decides when a set of displays will mirror, for example when connecting a projector or when a saved layout contains mirroring screens.
When the mirroring layout comes from a previously saved configuration, it's possible to reset the layout persistence by running the following script (administrator access required):http://www.displaylink.com/downloads/file?d=145
This mirroring issue needs to be resolved by Apple. To increase its priority, DisplayLink recommends to open a bug with Apple.
DisplayLink's own bug is tracked under ID 33650324. Apple's internal defect number for this issue is ID 26394372.