Permalink stops working for the latest post only about 15 minutes after publishing/editing

In our case, the issue was caused by a specific plugin, in this case it was the Google XML Sitemaps version 4.1.5, upgrading to 4.1.7 resolved the problem.

A bit of background: this non-profit site is highly seasonal and we usually upgrade and test everything before the 2-month peak season starts, and try to avoid plugin upgrades during this period as it’s challenging enough to deal with content. Once again it proved to be very useful to have a site mirror for testing and troubleshooting.