macOS High Sierra: Mirror issues

This article applies to macOS 10.13 - 10.13.3. For information on 10.13.4 see here.

macOS High Sierra 10.13-10.13.3 does not yet support mirroring of DisplayLink screens.

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):

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.

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