Thank you for your quick reply. Deleting the ACF plugin files didn’t restore the site, but restoring the database plus the plugin files did restore the site.
(It’s possible that solely restoring the database to its previous state would have allowed the site to be accessible again.)
For your future reference, only ACF was updated from 4.1.8 to 18.104.22.168; WordPress and other plugins were all up-to-date before the ACF update.
The site is up now, and we’ll determine if there was a conflict with another WordPress plugin, or if there’s code specific to the ACF 22.214.171.124 update that conflicted with the custom WordPress theme.
Updating ACF from 4.1.8 to 126.96.36.199 on another website proved successful.
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