(for me at least)
I had the same issue despite trying the Presonus website solutions.
Using newest UC version 18.104.22.168644, Win 10 laptop, UC finds the Audiobox iTwo but when I double-click it in the UC window nothing happens for a few seconds then the small windows appears saying that there is no or limited connectivity to the Audiobox.
Since the Audiobox iTwo only handles up to USB 2.0, I tried using USB 2.0 all the way. I used an older laptop with only USB 2.0-ports, a USB 2.0-cable running from the laptop to the Audiobox iTwo and everything worked. The Audibox iTwo showed up in UC and I finally managed to update my Audiobox iTwo to the latest firmware, 1.33.
EDIT: just for testing purposes I afterwards tried a USB 3.0-cable and it worked as well so the issue seems to the USB-ports of the computer hosting the UC app.