Group fields

Now you can setup rows and columns even on group fields too. First Create your cmb2 metabox with group fields like you are used to:

$prefix = '_yourprefix_group_';

$cmb_group = new_cmb2_box(array
(
    'id'           => $prefix . 'metabox',
    'title'        => __('Repeating Field Group', 'cmb2'),
    'object_types' => array('page',),
));

$field1 = $cmb_group->add_field(array
(
    'name' => __('Test Text', 'cmb2'),
    'desc' => __('field description (optional)', 'cmb2'),
    'id'   => $prefix . 'text',
    'type' => 'text',
));
$field2	= $cmb_group->add_field(array
(
    'name' => __('Test Text Small', 'cmb2'),
    'desc' => __('field description (optional)', 'cmb2'),
    'id'   => $prefix . 'textsmall',
    'type' => 'text',
));

// $group_field_id is the field id string, so in this case: $prefix . 'demo'
$group_field_id = $cmb_group->add_field(array
(
    'id'      => $prefix . 'demo',
    'type'    => 'group',
    'options' => array
    (
        'group_title'   => __('Entry {#}', 'cmb2'), // {#} gets replaced by row number
        'add_button'    => __('Add Another Entry', 'cmb2'),
        'remove_button' => __('Remove Entry', 'cmb2'),
        'sortable'      => true,
    ),
));
$gField1 = $cmb_group->add_group_field($group_field_id, array
(
    'name' => __('Entry Title', 'cmb2'),
    'id'   => 'title',
    'type' => 'text',
));
$gField2 = $cmb_group->add_group_field($group_field_id, array
(
    'name'        => __('Description', 'cmb2'),
    'description' => __('Write a short description for this entry', 'cmb2'),
    'id'          => 'description',
    'type'        => 'textarea_small',
));

Now pay attention to the addCmb2GroupGrid() method

if (!is_admin())
{
    return;
}

// Create a default grid
$cmb2Grid = new \Cmb2Grid\Grid\Cmb2Grid($cmb_group);

// Create now a Grid of group fields
$cmb2GroupGrid = $cmb2Grid->addCmb2GroupGrid($group_field_id);
$row           = $cmb2GroupGrid->addRow();
$row->addColumns(array($gField1, $gField2));

// Now setup your columns like you generally do, even with group fields
$row = $cmb2Grid->addRow();
$row->addColumns(array($field1, $field2));

$row = $cmb2Grid->addRow();
$row->addColumns(array($cmb2GroupGrid)); // Can be $group_field_id also