Count generated by model (through pivot table) not shown

I am trying to get the count of how many people participated in a scan. at this moment i need 2 counts:

• Total participants count
• Total finished count

i made a pivot table in Ember that holds specific data about the participant, like he finished the scan or not.

My model:

import DS from 'ember-data';

var inflector = Ember.Inflector.inflector;
inflector.irregular('scan', 'scan');

var scanModel = DS.Model.extend({
    title:               DS.attr('string'),
    mailInviteSubject:   DS.attr('string'),
    mailInviteMessage:   DS.attr('string'),
    mailResponseAddress: DS.attr('string'),
    dateDeadline:        DS.attr('date'),
    scanGroup:           DS.belongsTo('scanGroup',      {async: true}),
    questionGroups:      DS.hasMany('question-group',   {async: true}),


    /**
     * Participants
     */
    scanParticipants:            DS.hasMany('scanParticipants', {async: true}),
    participants:                Ember.computed('scanParticipants.@each.participant', function () {
        return this.get('scanParticipants').then(function(scanParticipants) {
            return scanParticipants.mapBy('participant');
        })
    }),
    participantsCount:           Ember.computed('scanParticipants.@each.participant', function () {
        return this.get('scanParticipants').then(function (participants) {
            return participants.get('length');
        });
    }),
    participantsCountFinished:   Ember.computed('scanParticipants', function () {
        return this.get('scanParticipants').then(function (participants) {
            return participants.filterBy('finished', true).get('length');
        });
    }),

    isClosed:        Ember.computed('dateDeadline', function () {
        let scanDate = moment(this.get('dateDeadline'));
        let date     = moment();

        if(scanDate < date)
            return true;
        else
            return false;
    }),
});

export default scanModel;

I have the following template:

<td>{{input type="checkbox" checked=isChecked action="scanChecked"}}</td>
<td>
    <h2>{{scan.title}}</h2>
    Verloopt op {{format-date scan.dateDeadline format="DD MMMM"}} <small class="_muted">({{#if scan.isClosed}}Afgerond{{else}}Over{{/if}} {{format-date scan.dateDeadline type='remaining'}} geleden)</small>
</td>
<td>
    <h2>{{scan.participantsCount}}</h2>
    <small class="_muted">uitgenodigd</small>
</td>
<td>
    <h2>{{scan.participantsCountFinished}}</h2>
    <small class="_muted">voltooid</small>
</td>
<td class="_align-right">
    {{#link-to 'scangroup.scan' scan.id class="btn btn-inverted btn-small"}}Bekijk{{/link-to}}
</td>

The problem now is, is that {{scan.participantsCount}} and{{scan.participantsCountFinished}} shows [Object Object] in my template instead of the counts.

But if i log the counts in the promise i get the good count that should be displayed in the template.

How does it come that it show's [Object Object] instead of the count, and how can i make it possible to show the count?

Thanks in advance!

Kindly regards,

Pascal