I recently purchased the UD-3900PDZ as an upgrade (prior user of the UD-ULTCDL and the UD-3900).
Since I received the dock I have experienced regular connection drops and screen freezing issues when using Surface Pro 2017 connected to the dock. I have 3 monitors connected.
While on Teams or GoToMeeting my sessions will freeze up and and disconnect, often leaving two of the monitors with frozen images from when the disconnect happened. The session sometimes reconnects but usually the screen arrangement display settings are lost or two of the screens remain frozen with the image fro when the session froze/disconnected. Disconnecting the Surface from the dock will leave the frozen images on 2 of the monitors.
The only way I’ve been able to recover is to unplug the power supply to the UD-3900PDZ and wait a few minutes to reconnect the power, then reboot and reconnect my Surface.
This has been extremely frustrating. I work remotley and am on video meetings and screen shares 7-8 hours per day.