Custom Bulk Actions handler not firing

Hi first fix your condition

if ( $action !== ‘out_of_stock’ || $action !== ‘in_stock’) {

this condition will always run because your action is in contrast with “out_of_stock” or “in_stock”. So I think if you change the condition from OR to AND it will work.

Then find out if the screen id is the one your looking for, and then modify your filter:
to understand what is your screen id, add this to your plugin or your theme function.php, and remember to remove it later:

add_filter( 'wc_product_has_unique_sku', '__return_false' );

add_action('init', 'test_function');
function test_function(){
    $value = get_current_screen();
    echo '<pre>';
    print_r($value);
    echo '</pre>';
}

then when you get the correct screen id, for instance SCREEN_ID, modify your filter like this:

add_filter( 'bulk_actions-SCREEN_ID', 'register_my_bulk_actions' );