Several times when going into screen lock mode, when I come back and unlock my MacBook Pro, one or more of my 3 external displays will be dark and repeated efforts to get it back fail until I disconnect the display from the StarTech USB dock, turn off the dock, wait a few seconds, turn on the dock and plug the display cord back into the dock.
This is frustrating to say the least. When this happens the screen arrangement goes completely wrong until I get the missing display active again. I'm running Mac OS X Mojave 10.14.3 and DisplayLink 5.0.1