wp_set_object_terms won’t work inside wp_insert_post hook in front end form (non admin page)

I have been trying this for days without any successs. I created a function in my child theme function.php. What I am trying to do is whenever a post gets saved or inserted, I want to update it’s category. The post and category are customs.

The code below is shortened and hardcoded for the purpose of the question.

add_action('wp_insert_post', 'custom_function_sync_category', 20);
function custom_function_sync_category($post_id){
$term_taxonomy_ids = wp_set_object_terms( 2446, 219, 'advert-category', true);
log($term_taxonomy_ids); //returns success
/* Log Output:
 Array
(
    [0] => 219
)
*/
//2446 is the postid
//219 the category should be assigned
}

So whenever I update/insert post in the admin area it works 100%.

When I update/insert post in the front end form (non-admin page), the functions gets triggered and it logs success but the category doesn’t get assigned.

If I hook this function to add_action('init', 'custom_function_sync_category', 20); It will work 100% on page refresh.

I don’t know what I am missing. Read many topics says move your function to init and yes it works but how will I be able to run this function on save_post / wp_insert_post to edit the saved/inserted post.

I tried using wp_set_post_terms but it doesn’t work also. Played with the priority from default to 999.

This is frustrating, keep thinking about this all day.

Appreciate any help,

Thank you in advance,