Hi Alan42,
Potentially, you experienced an issue related to Dell Uxxx monitors for which there is already a dedicated thread:
https://www.displaylink.org/forum/sh...ad.php?t=69652 ---> a fix for it is at works.
To confirm if this is the same problem, could you please check:
When Dell 23 is black, does the monitor recover if you disconnect and connect the cable that connect the dock and the monitor (DP cable)?
If possible, a workaround could be to connect this particular monitor using HDMI cable, while the engineering team is working on a proper fix.
Regards,
Szymon