You will need to create an action or filter that runs during the import, see this reference https://www.wpallimport.com/documentation/advanced/action-reference/ I’m not sure what filter to tell you to use here, but I think it would need to be “pmxi_saved_post”.
WPAI does not call update_field() when importing ACF fields, it calls update_post_meta() directly, so anything added by the plugin that creates the bidirectional fields will be bypassed.
So what you need to do is use the correct action/filter for WPAI and in your filter or action get the relationship field value and use update_field() to update that value which should cause the acf add on to perform it’s own actions to create the bidirectional entries needed.
