While navigating shape and distance of the next turn are missing after screenlock

I imported an GPX route and started navigation, the shape and distance of the next turn were shown in the left upper corner of the screen (see link) and the voice was telling what to do. But after a few minutes when the Android phone automatically has been gone on screen lock, in the left upper corner a question mark appears instead of shape and distance info and the lady (voice) is quiet too after removing screenlock.