I was just downloading the latest live and PTS updates on my MacBook Air and suddenly got disconnected with a message that the patch manifest file couldn't be found, or whatever that message says.
But I closed the ESO launcher, closed Steam, restarted Steam, restarted the ESO launcher, and now the downloads are going again-- albeit both of them starting over from 0%. So maybe the server went down for a moment and is back up now? I hope so, as I'm about to try getting on to play on my Windows PC while my MacBook Air updates.
... And I forgot that I can't play ESO on one computer if the launcher is open on another computer. Fortunately the update for the live server finished on my MacBook Air, so I can pause the PTS update and do it later.