always getting Infinity in geo_distance sorting

[SirCameron]

Question

I have an index:

{
      index: 'discoveries',
      mappings: {
        properties: {
          id: { type: 'integer' },
          description: { type: 'text' },
          location: { type: 'geo_point' },
        },
      },
    }

when I run a query like this:

      index: 'discoveries',
      query: {
        match: {
          description: {
            query: 'some text',
          },
        },
      },
      sort: [
        {
          _geo_distance: {
            location: [location.longitude, location.latitude],
            order: 'desc',
            unit: 'km',
            mode: 'median',
            distance_type: 'arc',
            ignore_unmapped: true,
          },
        },
      ],
    }

This always returns Infinity for the _geo_distance sort... always...
Has anyone else experienced this? is there something obvious I'm missing?