Jetpack, a very popular plugin that is used on millions of WordPress blogs has had some reports of fatal errors which can result in your entire website crashing. Version 11.5 was released yesterday and once the automatic updates goes ahead, it removes some important files related to the IP block/allow feature within the Firewall section of Jetpack. Once the upgrade is done, those files are missing and the website refuses to be accessible.
This very website (theinterface.uk) runs on WordPress and we use Jetpack too. This site was down this morning had displayed the fatal error message, getting it back online required us to log into the backend of the site via FTP, delete the Jetpack plugin and then reinstalling version 11.5 again. As of writing this post, Jetpack have released a patch to fix this issue in the form of 11.5.1.
Hey folks, thanks for all the reports! We’ll be conducting a point release, Jetpack 11.5.1 to address this within the next 24 hours.
The tldr is that the Firewall module (waf) autogenerates some files for the IP block/allow list that are getting removed in the upgrade and then missing when Jetpack looks for them later.
As some folks have mentioned, simply removing and re-installing Jetpack 11.5 will fix the issue in the meanwhile. If your site is down after upgrading, you can also try toggling the WAF module which should regenerate the needed files by using the WP CLI: wp jetpack module deactivate waf and then wp jetpack module activate waf.
More information can be found here on the Jetpack forum, and Jetpack 11.5.1 is out now for those looking to resolve this issue.