Thanks for sharing your experience here. Getting
404 responses from all URLs is indeed a strange happening, especially given that redeploying the same code rectified the issue. I've not heard of this happening to others thus far. I'm happy to hear this is no longer happening to you.
Should this ever happen again, I would strongly urge you to file a defect report on the
App Engine public issue tracker and provide as much information as possible such as the output of
curl --verbose to help us better identify the source of the problem.