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.
Sounds like a deployment problem. Speaking in generalities, code doesn't "sometimes" work unless it's written that way.. in which case it's working 100% of the time :)