This hotfix can be downloaded from the SFDC Customer Portal Web User Interface using your username and password for the TIBCO Support Web. Once logged on you can find the hotfix under the Downloads Menu:

"AvailableDownloads/Messaging/EMS/8.4.0/Hotfix-2.  Please read the Readme file for Instruction before to apply the hotfix.


Closed Issues in 8.4.0_HF-002 (This Release)

EMS-7323
  Fixed a defect in which the reconnection of a client after a fault-tolerance
  failover could cause another connection that was given the same ID in the
  meantime to be terminated. This could occur under rare circumstances and
  manifest in the server log as "reconnect detected: replacing active
  connection".  This defect affected Release 8.4.0.

EMS-7296
  Fixed a defect in which slow operations could interfere with the
  heartbeat protocol between the EMS server and clients, resulting in
  client disconnect.  This defect affected Releases 8.3.0 and 8.4.0.