Hey SRN2016, we have very similar macs and for me the problems seem to be finally gone. I did all sorts of troubleshooting on and off for several weeks, but some of the last things I did which coincided with the problems disappearing were
- rebuilding preferences of all Steinberg software
- rebuilding the soft e-licenser by using a special ELC installer available from Steinberg (I was not using the soft ELC however)
- Replacing the PRAM battery, which I probably should have done earlier anyway. This was because I found various posts suggesting a dying battery could affect low level functionality like USB so I thought why not.
For the last week I have had no issues, while before I would get ELC connection losses every 20 minutes or so when using any Steinberg software. I also bought a Sonnet USB 3 card and a new dongle and those work perfectly, but my problems disappeared before I got them.
Otherwise very happy with the performance of Mojave in general and Cubase 10 on my machine.