CMB2 Image Repeater to ACF Pro Repeater

functions.php

// PLEASE NOTE!
// I set my ACF Image Repeater to return only the image ID...
// So this may not work if you have it set to return an Object or...?
// I found this helpful: https://support.advancedcustomfields.com/forums/topic/repeater-update_field/

add_action( 'init', 'cmb2_to_acf' );

function cmb2_to_acf() {
	// You can use offset if needed.
	$args = array(
		'post_type'   => 'a_custom_post_type',
		'numberposts' => 100, // whatever number.
	);

	$my_posts = get_posts( $args );

	foreach ( $my_posts as $my_post ) {
		my_acf_save_post( $my_post->ID );
	}
}


function my_acf_save_post( $post_id ) {
	$meta = get_post_meta( $post_id );
	$field_key = 'field_5db205dacf56f';
	$data = unserialize( $meta['some_image_repeat'][0] ); // This is CMB2
	$value_array = [];
	$counter = 0;
	foreach ( $data as $d ) {
		$value_array[ $counter ] = array(
      // d['image_id'] is the image ID
			'field_5db205eecf570' => $d['image_id'],
		);
		$counter++;
	}

	update_field( $field_key, $value_array, $post_id );
}