functions.php

        add_action('cmb2_admin_init', function(){

            $cmb = new_cmb2_box([
                'id' => 'cmb_repeater_metabox',
                'title' => 'Repeateable groups',
            ]);

            $groups = $cmb->add_field([
                'id' => 'cmb_groups',
                'type' => 'group',
                'options' => [
                    'group_title' => 'Entry {#}',
                    'add_button' => 'Add another entry',
                    'remove_button' => 'Remove entry',
                    'sortable' => true,
                ],
            ]);

            $cmb->add_group_field(
                $groups,
                [
                    'id' => 'cmb_groups_image',
                    'name' => 'Image',
                    'type' => 'file',
                ]
            );

            $cmb->add_group_field(
                $groups,
                [
                    'id' => 'cmb_groups_text',
                    'name' => 'Text',
                    'type' => 'textarea_small'
                ]
            );

        });

        add_filter('lg_cmb2_modals', function ($metaboxFormIds) {
            $metaboxFormIds[] = 'cmb_repeater_metabox';

            return $metaboxFormIds;
        });

view.js

window["cmb_repeater_metabox_view"] = function (model) {
    console.log(model);

    return "REPEATABLE GROUPS";
};