I found where the problem was. Everything was working correctly, but I was uploading the wrong version of the php file in question. User error, indeed, but in the process I learned a lot about the WP cache.
cache reset button and question about deleting cache
There are essentially two very different cases how WP site typically bring server down with symptoms of CPU overload: Your site is not fast enough for your traffic Simply put if your server can serve page every tenth of a second and you get more than 10 pageviews in that second – your resources are … Read more
Major cache but only on WordPress site
My website resets when accessing the index page
Should I use transients for these API call results?
On your master site, register a new XML RPC method that accepts a date argument and replies back with all content published since then. For each of your drone sites, register a cron hook that pings the master every X minutes/hours with the date of the most recently “imported” content, and then saves the response … Read more
Super cache caches mobile pages for desktop
GravatarLocalCache Plugin Broken in WordPress 4.2
Having 4000 posts, my site is so slow