Bootstrap 4 - Checkbox not Working Properly inside Popover in Bootstrap Modal

There are two checkboxes inside popover in Bootstrap Modal. The fiddle is here.

HTML:

<div class="container-fluid">
    <div class="row">
        <div class="col-12">
            <button type="button" class="btn btn-primary open-modal" data-toggle="modal" data-target="#bs-modal">
            Open Modal
            </button>
            <div class="modal fade" id="bs-modal" tabindex="-1" role="dialog" aria-hidden="true">
                <div class="modal-dialog modal-lg" role="document">
                    <div class="modal-content">
                        <div class="modal-header">
                            <h5 class="modal-title" id="exampleModalLabel">Bootstrap 4 Modal</h5>
                            <button type="button" class="close" data-dismiss="modal" aria-label="Close">
                            <span aria-hidden="true">&times;</span>
                            </button>
                        </div>
                        <div class="modal-body">
                            <button type="button" class="btn btn-secondary btn-sm bs-popover" data-container="body" data-toggle="popover">
                            Show Popover
                            </button>
                            <div id="popover-content">
                                <div class="form-check">
                                    <input class="form-check-input" type="checkbox" value="1"
                                        id="default-checkbox" name="default-checkbox">
                                    <label class="form-check-label" for="default-checkbox">
                                    Default Checkbox
                                    </label>
                                </div>
                                <br>
                                <div class="custom-control custom-checkbox">
                                    <input type="checkbox" class="custom-control-input" id="custom-checkbox" name="custom-checkbox" value="2">
                                    <label class="custom-control-label" for="custom-checkbox">Custom Checkbox</label>
                                </div>
                            </div>
                        </div>
                        <div class="modal-footer">
                            <button type="button" class="btn btn-secondary" data-dismiss="modal">Close</button>
                            <button type="button" class="btn btn-primary">Save changes</button>
                        </div>
                    </div>
                </div>
            </div>
        </div>
    </div>
</div>

CSS:

.open-modal {
    margin: 20px;
}
.modal-body {
    min-height: 200px;
}
#popover-content {
    display: none;
}

JS:

$('.bs-popover').popover({
    html: true,
    content: function() {
        return $('#popover-content').html();
    },
    title: 'Popover Title'
});

1. Problem with Default Checkbox: I'm not able to check it by clicking the label.

2. Problem with Custom Checkbox: It cannot be checked.

Why is this happening? How can I fix it? Any help would be appreciated.