Magento 2: There are no commands defined in the “cron” namespace

Magento 2.4.3-p1

When I run bin/magento cron:run on the command line all is fine. No issues.

When I let it run by the system’s cron it does not work and I get this in the /var/log/magento.cron.log all the time: There are no commands defined in the "cron" namespace.

This happens to the same setup on two rather different systems (local dev environment and remote production).

I have other 2.4.3-p1 shops with the same local/remote setup without any issues.

I already checked the file permissions but nothing helps. Even a radical chmod -R 777 * does not make a difference.

I ran out of options. What could be the issue here?

Thank you

EDIT:

This ist the log entry in debug.log and system.log:

[2021-11-25 16:20:02] main.ERROR: There are no commands defined in the "cron" namespace.
#0 /vendor/symfony/console/Application.php(657): SymfonyComponentConsoleApplication->findNamespace('cron')
#1 /vendor/symfony/console/Application.php(237): SymfonyComponentConsoleApplication->find('cron:run')
#2 /vendor/magento/framework/Console/Cli.php(115): SymfonyComponentConsoleApplication->doRun(Object(SymfonyComponentConsoleInputArgvInput), Object(SymfonyComponentConsoleOutputConsoleOutput))
#3 /vendor/symfony/console/Application.php(149): MagentoFrameworkConsoleCli->doRun(Object(SymfonyComponentConsoleInputArgvInput), Object(SymfonyComponentConsoleOutputConsoleOutput))
#4 /bin/magento(23): SymfonyComponentConsoleApplication->run()