We are using a plugin (https://github.com/ADeMen/GOOVAIN/) that is supposed to provide a 'get shortlink' button along with some database updates.
It should look like this.
This worked perfectly for a while. We migrated our database and content to a new server. Now whenever we create or edit a post this option is missing, but only for the new posts. Existing posts are fine.
I edited the source of the plugin slightly - adding a fopen dumping the behavior of the plugin (when the file is opened, functions begun, etc) to the tmp directory for analysis. The file is opened, the add_* directives are called. The defined functions are never called.
The add_filter and add_action directives look right to me.
I've checked the syslog, httpd logs, php error log and nothing gives any explanation as to what the issue is or how to fix it.