Displays this message and navigation shuts down until SUV is shut off, sits a while, and is restarted - everything else works

Hi All - I'm new to this forum and unfortunately my first post is a problem;

My navigation screen shows "Navigation Fault" error message (photo attached) and navigation completely shuts down. Everything else works, including sync to iPhone and all other features. Sync is updated.
The problem is intermittent - but getting more frequent. Its not the phone connection. It will do it without a phone in the SUV.
Took it to the dealer - They said "Gee we have never seen this before!" and fooled around with it for a day but it would not do it at hte dealership.

I've tried everything I can think of - Has anyone else had this problem? Any thoughts that may help?
2017 Ford Edge Titanium with Sync 3.

Thanks
Tom