I finally create a new project and restore a backup of the Datastore and deploy our Rietveld version as App Engine.
The hostname with SSL is already active but I had to apply for a new OAuth consent screen which is limited for now to 100 users until it is verified in few days.
After some testing days, I will delete the previous and broken project.
New changeset 28c5e9522d06 by Cédric Krier in branch 'default':
Update email addresses for new rietveld instance
https://hg.tryton.org/tryton-tools/rev/28c5e9522d06
More information, I found that the initial project is working back again. And I think I understand why. When creating the new project, I accidentally saved the OAuth setup on the original project and I think this unblocked the problem. Now that it is working back, I setup the Datastore as readonly.
Now we have to wait more time for the OAuth validation because I put an icon and I can not remove it because of https://issuetracker.google.com/u/1/issues/158736319.
Cédric Krieradded 1 deleted label and removed 1 deleted label