Horizon not spawning processes after upgrade

Hello

My app worked fine with Laravel 9 and 10, but when I upgrade it to Laravel 11, Horizon stopped working correctly.

When I launch the artisan horizon command, with Supervisord or manually, everything looks ok, a artisan horizon:status displays "Horizon is running" and I can see the command in my server processes with the ps command.

But what I don't see are the subprocesses that the horizon command should launch. On my production app, there are a number of artisan horizon:supervisor subprocesses under Horizon, each one with a artisan horizon:work subprocess. On my test app with Laravel 11, nothing. And thus when I send something in the queue, it's not processed.

The .env and config files are the same. To upgrade to 11 I only needed to change composer.json and do a composer update , no changes to the app have been done as there's nothing to do.

If I rollback to Laravel 10 and reload Supervisord, my queues are back.

Any idea ?