Yesterday we were experiencing a degraded performance in the AppBuilder cloud build services. For some time, our clients were not able to build or publish for the iOS platform. I believe you have came across the very same issue, so please, excuse for the inconveniences it has caused. Everything should be up and running now. Please, let us know if you have any further issues.
Also, you can take a look at our status page
, as it is being updated as soon as a problem is detected. I hope it helps.