Logitech K520 wireless keyboard and mouse have periodic delays when connected to the USB2.0 ports on my UD-3900 DisplayLink. There doesn’t seem to be a problem if I plug it into the USB 3.0 port. Maybe this will be helpful for someone as it took me a bit to figure out it would work ok on the 3.0 port.
Thanks for getting in contact with us. There is a known issue between the USB 3.0 and wireless dongles for keyboards and mice. Essentially, USB 3.0 operates at the same frequency as the wireless signal, this interference can cause behavior like the periodic delays you were experiencing. For more details, you can read this article:
By moving the dongle away from the USB 2.0 ports on the back, you were moving the dongle away from the USB 3.0 cable that causes the interference.