Hi Russ, thanks for posting. Sorry to hear of the lag you are experiencing while our adapter is connected and I will be happy to help!
Thank you for the description of the behavior. Based off of your description, it sounds like you may be experiencing a wireless interference issue that can occur between any USB 3.0 device (not just our adapter) and the 2.4GHz wireless signal from the wireless receiver for keyboards and mice. Although a bit technical, Intel has written a paper of the behavior --> http://www.intel.com/content/www/us/e… When you connect the adapter to the USB 2.0 port, this will not happen as the electrical signal is not moving in a manner to create this interference; however, this would not be a viable test as the MS dock (assuming you are using this one --> https://www.microsoftstore.com/store/…) and Surface Pro 3 only have USB 3.0 ports.
Assuming that you have our adapter and the Logitech wireless USB receiver connected to one of the USB ports on the Surface Dock, would you be able to temporarily test moving the USB receiver to the USB port directly on your Surface Pro 3 in order to see if the interference continues?
If this test does not yield better results, there may not be much else we can suggest to resolve the lag. But I would be happy to examine some log files from the system to see if there is any other variable that can be checked that could attribute to the lag. To help me do so please download and run our diagnostic utility PlugDebug --> http://plugable.com/support/plugdebug with everything connected. Please send us the file that is created on your Desktop by attaching it to an email to our direct support email address at firstname.lastname@example.org with ‘Ticket Number 161632’ in the subject line so we can match everything up. We’ll then examine the logs and go from there.