MongoDB: not all the results are returned from a query, using $geoNear

I got this query :

 exports.search = (req, res) => {

  let lat1 = req.body.lat;
  let lon1 = req.body.lng;
  let page = req.body.page || 1;
  let perPage = req.body.perPage || 10;
  let radius = req.body.radius || 100000;


  var options = { page: page, limit: perPage, sortBy: { updatedDate: -1 } }

  let match = {}

  var aggregate = null;

  if (lat1 && lon1) {

    aggregate = Tutor.aggregate([
      {
        "$geoNear": {
          "near": {
            "type": "Point",
            "coordinates": [lon1, lat1]
          },
          "distanceField": "distance", // this calculated distance will be compared in next section
          "distanceMultiplier": 0.001,
          "spherical": true,
          "key": "loc",
          "maxDistance": radius
        }
      },
      {
        $match: match
      },
      { "$addFields": { "islt": { "$cond": [{ "$lt": ["$distance", "$range"] }, true, false] } } },
      { "$match": { "islt": true } },
      { "$project": { "islt": 0 } }
    ])
    // .allowDiskUse(true);
  } else {
    aggregate = Tutor.aggregate([
      {
        $match: match
      }
    ]);
  }



  Tutor
    .aggregatePaginate(aggregate, options, function (err, result, pageCount, count) {

      if (err) {
        console.log(err)
        return res.status(400).send(err);
      }
      else {

        var opts = [
          { path: 'levels', select: 'name' },
          { path: 'subjects', select: 'name' },
          { path: 'assos', select: 'name' }
        ];
        Tutor
          .populate(result, opts)
          .then(result2 => {
            return res.send({
              page: page,
              perPage: perPage,
              pageCount: pageCount,
              documentCount: count,
              tutors: result2
            });
          })
          .catch(err => {
            return res.status(400).send(err);
          });
      }
    })
};

The query is supposed to retrieve all the tutors in a given range (which is a field from the tutor model, an integer in km, indicating how far the tutor is willing to move) around a certain location. (lat1, lon1).

The issue is that all the documents are not returned. After many tests, I have noticed that only tutors that are less than approximatively 7.5km away from the location are returned and not the others. Even if the tutor is 10km away and has a range of 15km, he won't be returned as he is farer than 7.5km.

I have tried switching location between two tutors (one that is returned and one that is not but should be) to see if this is the only thing causing the issue and it is. After I switched their location (lng and loc), the one that was returned before is no longer and vice versa.

I really don't get why this is happening.

Also, I know the result size is less than 16MB since I don't get all the results, even with allowDiskUse:true.

If you have any other idea about why I'm not getting all the results, don't hesitate !

Thank you !

from MongoDB: not all the results are returned from a query, using $geoNear