[quote=]
There, the rerouting was enabled and was not triggered?
[/quote]
Yes, exactly. At this time navigation had been stopping working for maybe ~15min/~10Km.
Even after “stop/start navigation” no rerouting was triggered (as you can see on screenshot).
Later (at ~16:03) I stopped the app (double back) and started again.
After that the route was instantly recalculated and navigation was working again.
[quote=]
How was internet connection, any (spoken) warning?
[/quote]
Screenshot says 4g 
No warning I could remember of, and munich usually has excellent internet coverage.
Hmm, one thing that might be contributing:
The start point on the screenshot was the last time a successfull recalculation had been taken place.
After that I was traveling through a longer tunnel. So no GPS for some time (I think there has been a warning about missing GPS)
[quote=]
During all these, the screen was turned on or app was in background?
[/quote]
Screen was on and app in foreground the whole time from “point 1.” onwards.