@Brian-McG I carved out some time today and ran the route again. This time with a version where I added a 2 more shaping points as circled:
Screenshot (165).png
That did the trick, and Offline mode for the route worked. Waypoint #12 is too close after the turn, so I didn't get an audio announcement, but I was more concerned with simply forcing the turn on the correct street.
In the nutshell, Offline is functional, but the assumption I had regarding an MRA route calculating the same both online and offline (all the time) is incorrect. The lesson for me is to load up (or just plain overload) on shaping points to leave nothing to chance. I still think there should be some kind of alert when the calculations are different, but I feel comfortable continuing with offline navigation when needed. Thanks again for your input.