I guys, I have exactly the same issue (Ubuntu 16.04 / DisplayLink 1.4 driver).
I switch to the 1.3.54 driver, it's better but it's not enough at all...
I have a XPS 13,3" with Intel Core i7 (7th generation) + 16Go RAM and it's really slow slow... I'm very disappointed about the product/drivers.
DisplayLink Support Tool output :
https://wetransfer.com/downloads/48d...2114404/88ccf4