wp_set_post_terms doesnt work for WPUF

I have a WP User Frontend Plugin, so users can post via frontend.
Additionaly I have a custom taxonomy called board which is hierarchical.

I have found “WPUF Action Hook Taxonomy” for my problem https://gist.github.com/tareq1988/809ed96eaaf0ce5480e0

I can post successfully, but the choosen taxonomy from the dropdown will not be set. I checked the DB Table “wp_term_relationships”, there is no entry.

Seems like wp_set_post_terms is not working here and I dont know why. I already tried wp_set_object_terms with no success.

**Own_functions.php**

    /**
    * Add the input field to the form
    *
    * @param int $form_id
    * @param null|int $post_id
    * @param array $form_settings
    */
    
    function prefix_render_board_field( $form_id, $post_id, $form_settings ) {
        $selected = 0;
        if ( $post_id ) {
            $terms    = wp_get_post_terms( $post_id, 'board', array( 'fields' => 'ids' ) );
            $selected = ( is_array( $terms ) && count( $terms ) ) ? $terms['0'] : 0;
        }
        ?>
    
        <div class="wpuf-label">
            <label><?php _e( 'board', 'wpuf' ); ?></label>
        </div>
    
        <div class="wpuf-fields">
            <?php 
            $user_id = get_current_user_id();
    
            $board_parent_id = get_user_meta($user_id, "_Board Parent ID", true);
    
            wp_dropdown_categories( array(
                'show_option_none' => __( '- Select - ', 'wpuf' ),
                'taxonomy'         => 'board',
                'hide_empty'       => false,
                'name'             => 'board',
                'hierarchical'       => 1,
                'child_of'         =>$board_parent_id,
                'selected'         => $selected
    
            ) ); ?>
        </div>
        <?php

    }
    add_action( 'my_awesome_hook', 'prefix_render_board_field', 10, 3 );
    
    /**
     * Update the custom field when the form submits
     *
     * @param type $post_id
     */
    function prefix_update_board_field( $post_id ) {
        if ( isset( $_POST['board'] ) ) {
            wp_set_post_terms( $post_id, $_POST['board'], 'board' );
        }
    }
    add_action( 'wpuf_add_post_after_insert', 'prefix_update_board_field' );
    add_action( 'wpuf_edit_post_after_update', 'prefix_update_board_field' );

I am calling these hooks in the form:

   my_awesome_hook
    wpuf_edit_post_after_update
    wpuf_add_post_after_insert

Does anybody have a hint for me?

TIA