Hello, thanks for the detailed description. Seems like your application pool was recycled, because the following lines show us that SqlServerStorage class instance was re-created.
2014-09-15 05:33:50.3755 Info HangFire.BackgroundJobServer HangFire Server stopped.
2014-09-15 05:33:53.5161 Info HangFire.SqlServer.SqlServerStorage Start installing HangFire SQL objects...
You can enable Generate Recycle Event Log Entry settings for an application pool of your application to see what really is going on. After enabling these settings, your event log will include more details about application restarts.
