Nest has been doing some weird stuff last couple of days. I have seen the API not return any of the camera data for extended periods of time, etc.
Sorry for the troubles, it is hard at this point to understand what they have going on with all the server changes they are making.
Do make sure you are up to latest NST manager code. If you can catch logs of an issue we would like to see it via a private message.
Hopefully Nest will setting their servers down.