How does Up Ahead actually work?

I can't get the Up Ahead feature to work.

Whenever I load a course onto the watch with some waypoints, the watch displays them in Up Ahead before the tracking starts. I thought that once I pass each waypoint, the watch will go to the next waypoint.

However what actually happens is that when I start the tracking all waypoints disappear after a minute or two, and it only says "Finish x km".

I've searched everywhere but nothing useful came up.