I have the same problem for the last month or so. I used the voice feature 'Report Bug' to report the bug but should email. I thought this would be a known issue and they would be working on it and is caused by the new maps. I say new maps because i also saw a message that maps are updated on my screen.
After last firmware update about 2 months ago my NAV on the big screen is broken and is useless.
It doesn't refresh properly when I zoom-in or zoom-out (don't redraw the route), or when NAV recalculate the route it shows the old and new route at the same time.
Basically the NAV on the main screen is useless at this point, the small NAV next to the speedometer works fine, however at first was very confusing until I learn to ignore the big screen because I used to look at the big screen which was different from the Text To Speech or the screen next to the speedometer.
I tried restarting the console but still no luck.
Is this a known issue? or only happening on my car?