How WP-Cron works, and why it misbehaves

WordPress does not use your server’s real clock-based scheduler by default. Instead, on each page load it checks whether any scheduled task is due and, if so, fires it. That has two failure modes:

• Low-traffic sites: if nobody visits, nothing fires. Emails, syncs and cleanups run late or never.
• High-traffic sites: many simultaneous visits can each try to run the same heavy task, causing overlapping runs, database contention and CPU spikes.

Cron Monitor addresses both ends of that spectrum, and gives you visibility into what is actually happening.