wp_set_object_terms() custom taxonomy not working correctly when using insert post

I’m using wp_set_object_terms($postId, Array('tag1','tag2','tag3'), 'customtaxonomy');
with wp_insert_post to automatically create a new post.
it will show as

But on wordpress editor it is separated not like combined together as the image above, what I do to fix this is I only need to manually published or click the update button of editor to make them separated

I’m not really sure why it is acting like this?