The event you want is called 'Move file' rather than rename.
I can't think why it should have anything to do with the extension of the file, though our tester has just reported that she's seeing different behaviour depending on the size. Could that be the problem?
Regarding the upload event. The upload event would've triggered when the upload was completed, but at that point the name of the file was XYZ.filepart and therefore didn't match your file filter. I guess you could change your file filter to also match .filepart; that way you won't have to worry about the move event. You can do this using a regular expression as follows:
regex:/GUHealth/FromAU/GUHEALTH*\.csv(\.filepart)?
The brackets around the last extension followed by the question-mark indicate that it's optional.