To be clear, there's no connection between the debugging ip address list and the writing of errors to the logs. There's also nothing that makes some errors in a given app get logged but not others (more on that in a moment).
I appreciate you may be grasping at any possible straw. Here are some others to consider:
- When you get the error on the server with "no logging", what do you se on screen? Anything? Nothing? A blue ball?
- Do you have a site-wide error handler defined in the cf admin's first settings page? What is its value, for both servers? It may be that THAT error handler is intercepting errors and thus not causing them to be logged.
- Indeed, if you have ANY error handling (there, or at the app level--with onerror or cferror, or at the code level with try/catch), such error handling will prevent logging of an error....unless you choose to log it in the error handler itself, using cflog.
Sometimes people relying solely on errors appearing in the log are caught out by such error handling which can prevent it.
Please let us know if you confirm the above happening either way.