WordPress 4.9 “Tipton” was released last week and although it’s largely trouble-free, there is one particular issue users and developers are running into that’s causing frustration. In 4.9, custom page templates that are created fail to display in the Template drop-down menu. The issue is related to changes made to the file editor.
Previous versions of WordPress listed files 2-levels deep in the editor. In 4.9, the entire directory tree for a theme is listed regardless of its depth. Caching was added to help limit the performance impacts of loading large WordPress themes. “An unintended side effect of the caching is that the same directory listing function get_files is used both for the theme editor and for gathering page templates,” Weston Ruter, Co-Release Lead for WordPress 4.9 said.
Within the trac ticket, developers suggests that a button be added that flushes all caches or disabling the cache if WP_DEBUG is set to true. Neither suggestion turned into a patch committed to core. Instead, Ruter has released a plugin as a workaround that flushes the template cache. Other workarounds include, bumping the theme’s version, running the wp cache flush command in WP CLI, or waiting 60 minutes for the cache to expire.
The ticket is marked as a high priority but because of the upcoming holidays in the US and WordCamp US next weekend, it could be at least a few weeks before WordPress 4.9.1 is released.
And how about this bug? The editor does not seem to work on many websites on active themes and plugins https://wordpress.org/support/topic/cant-edit-main-theme-php-files-after-upgrading-to-4-9/