Thank you all for your input. I have found the source of my headaches.

I decided to print mkdir and rename commands out to a file and execute the list of commands from that file and noticed something weird.

The $filename and $dir_path variables contained unreadable characters, which did not print out during the execution of the script, but did print out to a file. Using regular expressions, I was able to remove the unwanted characters.. and so far so good! Everything is being renamed as it should. Thanks again all for your input.