Turn by turn directions working intermittently

I have my Edge 840 always up-to-date with newest maps installed via Garmin Express.

Yet, regardless the way I create a route (via Garmin Connect or Strava), turn by turn directions are working properly from the start, then at some random point they stop working (only track is visible on the map) and start working again at another random point.

Reloading the course does not help.

Is there any way I can fix it?

Cheers,
Lukasz