Hello,
I have come across this Bitnami Community thread which has discussed similar issues like yours. The thread has suggested launching a new WordPress instance, and migrating the desired content there.
This guide explains how to migrate a Wordpress instance and for maintaining the public IP, you should use static IP addresses. This document explains how to do that.
I have noticed this issue is more similar to Compute Engine than App Engine. I have also noticed you have created this StackOverflow thread for the same issue where you have already responded as well.
In case there are any technical issues or you would like to request any feature you can report it at the Public Issues by selecting the right component here.
Please also note that Google Groups forum is meant for general discussion of the platform, not specific technical issues. You can find more info about Community Support Overview on Google Groups here.