I found myself completely offline - no wifi or phone service. Starting spotify results in a blank screen with no access to settings, so I'm unable to turn offline mode on. Force stopping the app or clearing the cache make no difference. Just a blank screen.
As soon as I got back online I could access the app and change to offline mode. Stopping all network access and starting spotify up again works fine and I'm sure it'll be ok for the next 30 days in offline mode.
Am I missing something obvious here? Unless you're online you can't turn on offline mode. When you're offline you can't load the app and access settings.