I tried re-installing the DisplayLink drivers from the link on plugable.com/products/ud-3900. No luck.
After DisplayLink update to UD-3900, neither of my external monitors are connecting. They are not even recognized.
We worked with Les via our email ticketing system to resolve this issue. For the benefit of others who may be researching similar issues, here are the steps that were tried:
-Uninstall DisplayLink drivers
-Power-cycle the dock
It seemed in this case that power-cycling the dock did the trick.