A known issue on Mac OSX 10.13.4 and newer with the Displaylink software causes a tablet pen not to function and causes the display to be blank on the DTU-1031, DTU-1031X, and DTU-1141 tablets.
To resolve this issue please update the version of Displaylink software to version 4.3. beta 6 or newer which can be found online here: http://www.displaylink.com/downloads/macos