Kind of obvious that if the launcher has detected that it's offline, it should not even be attempting to contact an authentication server?

It hangs at this point and does not appear to be running a time-out timer.

Searching similar bugs the advice is to "first log in online". Well I most recently logged in online no more than 18 hours ago.

Also the Latest Log file is not populated. (Maybe only Minecraft proper populates the log, not the launcher?)