My guess is that this would be due to them deleting certificates from staging on Nov. 15.
You should be able to issue new certificates for the failing ones and have them work. If you're going to be utilizing staging extensively, you probably want to subscribe to the API Announcements category to get these sorts of notifications. They don't erase staging very often, but when they do it tends to confuse some people using it a lot like it did you. 
You may also want to read through the explanation of how they expect staging to be used, and their promises (or lack thereof) for the data there: