When getting fields from another post you need to supply the post ID of the post you want to get them from. In the case of a repeater, this only needs to be done for the top level field
if (have_rows('repeater_field', $post_id)) {
while (have_rows('repeater_field', $post_id)) {
the_row();
get_sub_field('sub_field_name');
}
}
More information here https://www.advancedcustomfields.com/resources/how-to-get-values-from-another-post/
