If using Message Journaling with HA (Replicated or Shared), the EnableJournaling flag must be enabled at both the PRIMARY as well as the SECONDARY HA servers beforehand to avoid any message loss during failovers.
This is because, when the EnableJournaling flag is enabled through online/offline mode on a queue which is in the ACTIVE server, the configurations will not be replicated to the PASSIVE server. The journaling status for the queue in the PASSIVE server will remain false. Untill Journaling is enabled for the Queue in the 'ONCE PASSIVE NOW ACTIVE' server, the messages that are sent to this queue are not 'journaled' and message losses can be observed in the Journaling Queue. Therefore, the flag must be enabled, explicitly, prior to starting the servers to avoid message losses.
This can be done by making the following changes in the Configs.cfg file of both the HA servers. This is the block defining the destination parameters for the queue 'PRIMARYQUEUE'.