Hi Marta,

I see you try to write it to a GPX, readable by garmin (for example)?

I think to make this work, you also need the TrackPoints that come with a GPX normally.  

See my attached example :) 

I tried to reproduce this and it works as expected.

Any errors in the log?

Maybe the source crs is not correct?

Working sample attached.

Ah, this is caused by the attribute track_id. From the documentation.

WayPoint features must have point geometry, or they will be ignored. The elevation attribute on WayPoint features will be ignored. Instead, the z-value of the point geometry will be used.

Route and Track features are handled according to the following process:

1. If the Route / Track has a route_id / track_id attribute, its geometry will be ignored. The route / track geometry will be written out based on the RoutePoint / TrackPoint features which share the same route_id / track_id value.
2. If the Route / Track has no route_id / track_id attribute, the geometry will be split up into RoutePoint / TrackPoint features. These point features will have no attribution.

Adding the trackpoints with the same track_id will solve the issue, as mentioned by @jobvdnoort 

I have managed to save the polygon as gpx and it looks fine in FME. But when added to gps I have odd lines. Images attached. Why do I have that extra lines?

How did you do this? Using Track only or Track and TrackPoints? Because if you use TrackPoints, the geometry of track will be ignored and the track is build from the trackpoints. Because of this the order of the trackpoints entering the writer does matter.

I have removed Points and it worked with Track only