Saw this just now on my corp account. I *think* I've seen it before, but it went away by itself somehow (maybe Chrome restart?).
chrome://settings/people and chrome://settings/syncSetup don't show any error.

sync-internals:   https://screenshot.googleplex.com/Ukyi5nqPWvD
signin-internals: https://screenshot.googleplex.com/CERBby3B9SC

Sync-internals shows several instances of a NETWORK_CONNECTION_UNAVAILABLE error. That doesn't sound plausible; this machine is connected to the (wired) corp network.
According to signin-internals, Sync's access token expired yesterday.
Looks like either the server sends an inappropriate response, or we're misinterpreting the response.