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MIDI Life Crisis wrote: The WiFi on this Mac Pro has never worked correctly and only rarely can I connect to my AT&T Uverse router, so I usually leave WiFi turned off. I tried a new router (or course it wouldn't even connect to the AT&T modem effectively) and had turned on WiFi on the mac, but forgot to turn it off. I noticed that it was on and as soon as I toggled it off, the MTP2 came back to life and is now as sprightly as the day it was born.

Hope that is helpful to others.

This rings a bell...
Could the order of the Services/Connections in Preferences>Network have something to do with this?
Have you tried creating a new BT or WiFi connection?

I had a similar problem on the new Mini. I read that the wifi and USB3 interfere with each other so that neither worked well and in my case, both experienced a lot of interruptions. This caused problems with BT too, with devices not appearing to the computer and connections not being made on startup. The solution often offered that worked for me was to use 5G wifi, and position USB3 devices away from the computer itself. I put the USB3 devices on a shelf on a shelf under the back of the desk. BT was still touchy, but I've changed to only wired mouse, pads, keyboards, and noticed better response when editing in the SE (also with Logic, Mixbus, etc), so BT is no longer on.