I have a similar computer but I connect my dongle via the USB ports on the Apple wired keyboard without issue. Assuming you don’t want to change your keyboard, have you tried using a passive USB hub connected to the Mac Pro?
No problems here on an iMac with USB 3.
I plug the dongle directly in and run everything else from a powered D-Link hub, model DUB-H7.
The dongle does work on this particular powered hub too just for info.
Unfortunately this does mean yet another power supply of course!
No problem here with the latest Mac Pro. I have had both a Steinberg dongle and an iLok plugged into the USB ports for a year now without incident. Actually I’d avoid using a hub for the dongles, and also suggest that you consider your problem may also be an indication that your dongle is starting to fail. The latter has been suggested numerous times previously.