I have the very same issue on my Dell XPS 13 9380 with a fresh Ubuntu 20.04.1 installation. It works well as long as the laptop display is in use. When I turn off the laptop display and want to use only the two monitors attached to my USB-C dock, the system becomes unusable.
* OpenGL version string: 4.6 (Compatibility Profile) Mesa 20.1.5 - kisak-mesa PPA
* DisplayLink 5.3.1
It worked well on the same machine using Ubuntu 18.04.
*Fix*
Applying the XServer patch seems to solve the problem:
https://www.displaylink.org/forum/sh...ad.php?t=67148