Thank you for posting! I am sorry things are not working as expected while using your Plugable UD-3900 docking station and I would be happy to help.
Thank you as well for the detail you provided that is much appreciated.
A few quick notes…
You mention that, “The dock’s firmware version is DisplayLink 8.6.1289.0 updated using the UD-3X00_9095_28 updater today.”
The ‘DisplayLink 8.6.1289.0’ item you mention is actually the version of the dock’s required DisplayLink software driver, it does not refer to the dock’s internal firmware. As this writing, this is not the latest version of the driver we recommend for our DisplayLink-based products. The latest version we recommend (which at present is 9.2 M3) is available from here --> https://plugable.com/drivers/displaylink
The ‘UD-3X00_9095_28 updater’ you mention is intended to update the dock’s internal USB 3.0 hub firmware to the latest version, which is 90.95. Any UD-3900 dock made within the last four years already has this update applied from the factory, so I would not expect you to need an upgrade.
A quick question regarding the behavior you describe…
Does the mouse pointer lag behavior occur only within the AutoCAD application? To put that another way, if you have a web browser window (for example Google Chrome or Mozilla Firefox) open within a display connected to the dock, does the mouse pointer travel properly and as expected?
Apologies if the question appears in any way redundant, however the intent is to determine if the behavior you describe is application specific.
Apologies again for the frustration, and thank you for giving us the chance to help!