Fatal error

Fatal error after updating to the actual last version:

Fatal error: Uncaught Error: Class 'ActionScheduler_Lock' not found in /path/wp-content/plugins/newsletter-optin-box/includes/libraries/action-scheduler/classes/abstracts/ActionScheduler.php:27 Stack trace: #0 /path/wp-content/plugins/newsletter-optin-box/includes/libraries/action-scheduler/classes/ActionScheduler_QueueRunner.php(104): ActionScheduler::lock() #1 /path/wp-includes/class-wp-hook.php(307): ActionScheduler_QueueRunner->maybe_dispatch_async_request('') #2 /path/wp-includes/class-wp-hook.php(331): WP_Hook->apply_filters(NULL, Array) #3 /path/wp-includes/plugin.php(474): WP_Hook->do_action(Array) #4 /path/wp-includes/load.php(1100): do_action('shutdown') #5 [internal function]: shutdown_action_hook() #6 {main} thrown in /path/wp-content/plugins/newsletter-optin-box/includes/libraries/action-scheduler/classes/abstracts/ActionScheduler.php on line 27