Action Scheduler failed to schedule Used CSS jobs

The Action Scheduler tries to queue a background task that generates the CSS used on each page. The task fails when the scheduler cannot create a new action. This happens because the cron system does not run, PHP stops the process, the database table is damaged, or the plugin cannot write the CSS file.

The failure stops critical CSS generation and slows page rendering. It also produces admin notices and log entries that reference the Used CSS hook.