I am making progress and have a suspicion…
To make things are generally working right, I was able to do a midi mix down of the demo “Lucky Seven” and open in Notion. All 3 midi tracks exported fine so confirming that Cubasis and Notion work fully in this area.
In my original project with the troubling midi issues, I am now suspicious that my desired midi track to export must have some midi file structure problem with it, that is causing Notion failure to open. I do remember moving and gluing another midi event onto the end of my desired midi track before exporting to Notion. This glued track still plays fine in Cubasis but won’t open in Notion, so I think my “glue job” mucked the structure of the resultant midi file.
I’ll have to play around more with the earlier project versions.