Versions 2.1.0 and later of the EMS Appliance are affected by Known Issue EMS-6829: when message swapping is disabled in a fault-tolerant configuration, persistent messages that have been sent to an EMS instance before a failover may be delivered to consumers with an empty body after the failover.

Workaround: make sure that the Message Swapping server property stays enabled (the default).

Note: If you are currently setting message swapping to be disabled for performance reasons, you can achieve the same effect by setting the Maximum Message Memory and the Destination Backlog Swapout server properties to values large enough to handle your maximum expected backlog. Note that swapping starts when the memory utilized by the active EMS server reaches 3/4 of the Maximum Message Memory property.