CodeIgniter Debug Bar

I think you can't overwrite core libaries with 'third-party' directory.

In the CI 3 doc :

Replacing Native Libraries with Your Versions
Simply by naming your class files identically to a native library will cause CodeIgniter to use it instead of the native one. To use this feature you must name the file and the class declaration exactly the same as the native library. For example, to replace the native Email library you’ll create a file named application/libraries/Email.php

http://www.codeigniter.com/userguide3/ge...aries.html

I had the same problem and rewrite my library profiler in application/libraries/Profiler.php. Now, everything works fine.