OK, thanks @idefix37

Enter coordinate -53,178.
Open menu, select distance planning.
Place first position somewhere at longitudinal 175E, second at 177E, next at 177W and 160W.
Select boat.
The pointer that shows the position on the route now is only visible in either east or west section of the route.
In case of moving the map to the left, the longitudinal position that in indicated east (e.g. 170W) will change to 170W as well. It might be another UI glitch. See last pic.

There is a UI glitch or bug while using the distance planning across the 180° of longitude.
The position pointer will either be shown in the east or west part of the route. Not over the complete route as usual.

Tested with
Firefox 111.0 and 112.0b2
Opera 96.0.4693.50
Edge 111.0.1661.41