Trying to run only certain action-scheduler tasks from WP-CLI

Question

I'm writing a plugin that performs several actions, one of which is a complex routine that parses and imports a large Excel spreadsheet (don't ask). I want this routine to run as a background task, using the action-scheduler plugin, to avoid UI sluggishness and server timeouts.

Specifically, I want to run this action using wp-cli and the server's cron instead of WP-Cron because, when run using WP-Cron, the server kills the task after about a minute of processing.

Here's the salient portions of my code (function names have been changed):

From the __construct method of my importer class:

add_action(
    'myplugin_background_file_import', 
    array($this, 'my_long_import_routine'), 
    PHP_INT_MAX, // lowest possible priority
    8 // argument count
); 

// ignore this hook so I can run it via server cron

add_action('action_scheduler_before_execute', function ($action_id) {
    $action = ActionScheduler::store()->fetch_action($action_id);
    $hook = $action->get_hook();
    if ('myplugin_background_file_import' === $hook) {
        error_log('ActionScheduler — skipping action hook: ' . $hook);
        throw new Exception('Skipping this action as it is handled by server cron.');
    }
});

// much later in a different method //

as_enqueue_async_action(
    'myplugin_background_file_import', 
    array(/* associative array of the 8 args previously mentioned */), 
    'my_group', 
    false, 
    255
);

The task scheduling works correctly (screenshot) and the action_scheduler_before_execute action filters the hook correctly, so WP-Cron does not run it.

The trouble is when I run this command, I don't get the expected result:

wp action-scheduler run --hooks="myplugin_background_file_import"

It will tell me that several tasks compete (from dozens to several hundred, depending on when I run it—it varies unpredictably), but the task in Scheduled Actions stays at "pending" no matter what I do.

Near as I can tell, I'm doing everything correctly. Am I incorrect? Is there a logic error here that I'm missing? This is my first serious use of action-scheduler so I'm definitely not ruling out user error.

Any input would be appreciated; if I've left anything out or can add more context, please let me know. Thanks!