The cron event list could not be saved

messages like Cron unschedule event error for hook ... were added to WordPress core recently, and are not a PHP error or warning, but are intentionally logged by WordPress. It does also appear to be a race condition, and has been an issue in WordPress for years, but has just happened silently — for at least Wordfence’s cron jobs, it’s not harmful.

The issue is basically that WordPress can sometimes start two copies of wp-cron to run the same jobs, triggered by multiple hits on the site starting close together, because wp-cron’s locking is imperfect — the jobs may run twice, but when one finishes, it updates the list of cron jobs, and then when the other finishes, it’s unable to make the same update, because it’s already done.

Ultimately, the Cron ran properly and there is nothing to worry about!

Thanks,

Joshua