Question: I recently deployed my app engine app and when I went to check it, the css was not showing in Chrome or in my Iphone Safari browser. I simply redeployed (no code changes at all) and now the site is running fine. What is going on here? Is this a bug, or is something wrong with my code but only sometimes?

Answer: 
I am experiencing the same issue, sometimes css - sometimes not Interestingly enough, if I use chrome, and select "Request Desktop Site" from the menu, my css loads fine.

I would assume this is something to do with the headers sent in the request, specifying the browser to be mobile.

I'll investigate further and update my answer when I have a solid solution, just a bit of food for thought for now.
This has happened to me when the css is cached and out of date. Your browser cannot detect that the css file has changed, and doesn't bother reloading it. Could it be that the CSS showed up the second time, not because you redeployed, but because your browsers were refreshed?