Today, on a site, I was unable to save new scheduled events. There were no errors in the code, no errors returned by wp_schedule_event(), and no errors recorded by PHP.
The issue was another plugin not able to get some expected data (and usually available) and scheduling an event and spawning the cron on each admin page load.
(They’re already fixing that in the next release)
Why that was interfering with the scheduling of new events is a bit more complicated to explain…
Hopefully, I was able to install the Monitor plugin, and just activating the “cron” monitor and reloading the overview page, the problem was super evident.
The ability to monitor and log core behavior of a software is something no one can miss. Having just a snapshot of what happened during a page load is most of the time insufficient. Only the history of the events can tell the whole story.
The Monitor plugin can be of great help with that (of course, I wrote it to have a tool when diagnosing a site’s unclear problems). And when uninstalled, it leaves no traces.
