Whenever I connect my MacBook Pro to the TBT3-UDV dock, the displays go into mirror mode. I then have to go into System Preferences to deselect mirror mode. It has just recently started doing this automatic reversion to mirror mode.
I’m using a Dell U3415W as the external display, and the MacBook built-in display.
Thanks for reaching out to us, I am sorry the system is defaulting to mirrored mode.
The mirroring setting is controlled inside of MacOS itself, normally the system will recognize the display’s previous setting and use the same format for the display when reconnected. However it the display is not communicating with the system it may be detecting it as a new display on connection.
The first step is to reset the monitor, docking station and MacBook to see if this helps to resolve this issue, please start by disconnecting the monitor from the docking station and its power supply, then press and hold the power button on the monitor for 30-60 seconds to reset the settings. To reset the docking station, disconnect the Thunderbolt 3 cable from the system and unplug the docking station from the power supply, let it sit for 30-60 seconds to fully discharge. Restart the MacBook and reconnect the docking station and monitor, please let me know if this helps, if not we can go from here.