I just finally got off the phone with tech support. I've had PDF driver issues before, so we thoroughly investigated that. After a while, we tried on the other machine that was working yesterday, only to have the same issue.The error log showed 502-504 bad gateway errors.

While resetting our modem, the tech discovered that many more calls were coming in for the same error. So it's now a known issue, engineers are on it, & they said try again in an hour or so. There is an investigation on it now & if it becomes even more widespread, they'll put out an alert to all users & update us when it's repaired.

At least they're taking it seriously & working to get it fixed!