Having exactly the same problem. Ubuntu 20.04.2 LTS, latest drivers installed, AMD Ryzen 3. Laptop works perfectly until I plug into the dock station, then it really slows down, everything jittering. DisplayLinkManager shows as running well over 100% CPU (between 130 and 180) if I do anything on the connected monitors. Been like this for about a year now, it's completely unusable. I've seen so many other posts on here with the same issue, unfortunately just being completely ignored!!