Crossing lines when displaying multilinestring from GeoJSON in Leaflet

Question

I'm stuck with something simple. I'm trying to draw a multilinestring from a GeoJSON file in a Leaflet map. I've taken the GeoJSON data from an application (built with OpenLayers + GeoServer), which is not mine, but the path I want to draw is exactly the same, so those coordinates serve my purpose.

First thing I don't understand is what are all those numbers that appear after longitude and latitude:

{"type":"MultiLineString","coordinates":[[[17.64145777,40.50170982,0],[4.42581744,11.11602236,4519487.27618627],[4.51125612,0,1232693.68416716],[42.92545724,0,0],

If I use the GeoJSON as it is, it shows strange results. See it here: https://codepen.io/Kata3890/pen/gOdmdRq

I tried to get rid of those numbers and use only the long/lat coordinates:

"type":"MultiLineString",
        "coordinates":[
           [
              [
                 17.64145777,
                 40.50170982
              ],
              [
                 17.64256586,
                 40.50200452
              ],

but then again the result is a bunch of crossing lines and gaps in the line when I zoom the map: See it here: https://codepen.io/Kata3890/pen/yLxMxPJ

What is wrong here?

Edit: image of how the path should look like:

Answer 1

I managed to partly resolve the mystery of GeoJSON returned by WFS service. There are still some coordinates missing, but that's probably consequence of some configuration error on GeoServer.

First I called WFS without srsName=epsg:4326 parameter and got the following result:

{
  "type": "FeatureCollection",
  "totalFeatures": 439,
  "features": [
    {
      "type": "Feature",
      "id": "vw_appia_cammino.fid-33ff99b0_186a32cb3fd_222b",
      "geometry": {
        "type": "MultiLineString",
        "coordinates": [
          [
            [
              1232637.59780902,
              4519475.4590854,
              0
            ],
            [
              0,
              1232662.16392913,
              4519487.27618627
            ],
            [
              0,
              0,
              1232693.68416716
            ],
            [
              4519502.58434888,
              0,
              0
            ],
            [
              1232728.41700269,
              4519517.51341278,
              0
            ],
.
.
.
  "crs": {
    "type": "name",
    "properties": {
      "name": "urn:ogc:def:crs:EPSG::32632"
    }
  }
}

There is obviously some error in coordinates returned. It seems like third coordinate is inserted and then coordinates are somehow shifted, and this cyclically repeats every four coordinates.

If coordinates are cleaned up and converted from EPSG::32632 to EPSG:4326 with proj4.js with this code:

road.features.forEach(function(feature) {
  var coords = feature.geometry.coordinates;
  coords.forEach(function(lineCoords, k) {
    var newLineCoords = [];
    var newCoord;
    for (var i = 0; i < lineCoords.length; i += 4) {
      newCoord = [];
      newCoord[0] = lineCoords[i][0];
      newCoord[1] = lineCoords[i][1];
      newLineCoords.push(newCoord);
      if ((i + 1) == lineCoords.length) break;
      newCoord = [];
      newCoord[0] = lineCoords[i + 1][1];
      newCoord[1] = lineCoords[i + 1][2];
      newLineCoords.push(newCoord);
      if ((i + 3) >= lineCoords.length) break;
      newCoord = [];
      newCoord[0] = lineCoords[i + 2][2];
      newCoord[1] = lineCoords[i + 3][0];
      newLineCoords.push(newCoord);
    }
    coords[k] = newLineCoords;
  }); 
});

var epsg32632 = new L.Proj.CRS('EPSG:32632','+proj=utm +zone=32 +datum=WGS84 +units=m +no_defs +type=crs');

function coordsToLatLng(coords) {
  var latLng = epsg32632.unproject(L.point(coords[0], coords[1]));
  return latLng;
};

L.geoJson(road, {
   coordsToLatLng: coordsToLatLng,
   style: function (feature) {
       return {
         stroke: true,
         color: "red", 
         weight: 5};
   }
}).addTo(map);

then result seems OK, excepts for coordinates missing at the end of sections, which is probably consequence of mentioned coordinate shift: