Complex polygon visualisation

I am trying to display a very large and complex extruded GeoJSON polygon, roughly the shape of Switzerland, with Cesium. the polygon has almost 20000 coordinates.

I am seeing my large polygon displayed in 3D but it has some strange lines going across it (please see screenshot).

If I manually chop off a side of the polygon, the problem disappears. I don’t know why. Is anyone able to shed some light here?

Thanks in advance!
result_emptiedTimeSlice_onlyOneAirspace.geojson (931.1 KB)

This looks like the order of one or some of the coordinates may be incorrect.

Does this render correctly if it’s not extruded? What does it look like in other viewers, like QGIS?

Will be a hell of a job to find out if something is up with the coordinate order but I will have to check that now!

If I remove the extrusion it looks fine. Could it be a bug in Cesium?

It looks fine in other viewers I tried, albeit only 2D viewers:, openlayers.
I have not yet tried it in QGIS.

Thanks for your reply. Some good suggestions to keep investigating.