Ok. Finally, Native 3.01 is working. I'm not sure why but my guess is that, having done a "security upgrade" for Mojave, that somehow fixed the problem. Here's a link tot he upgrade page: https://support.apple.com/en-ca/HT201222. Again, I don't know if this is what fixed it but ...
As a side note, Line 6 was very helpful with this problem. They emailed me several times with questions and even got in touch with Steinberg for their input.
Cheers,
Keith