Hello,
From the information you have given me, I don’t know what language you are using or if you are using app engine standard or flex. This Stack overflow link may be helpful at the moment of troubleshooting this issue you are having with not seeing the exported csv. However depending on the language you are using, you may need to adapt the information. Also, as a general information, here is our documentation on how to read/write to Google Cloud Storage. Now, when exporting to Google Drive, you need to use the Google Drive Api and you can see guides about how to do this in python and java. I would recommend you to make sure you are being properly authenticated which can be a common issue.
If you require additional help with troubleshooting the exporting of your csv file from your App Engine Application to Cloud Storage or Google Drive, please go to Stack overflow as Google Groups is meant for conceptual questions and discussions.