The Expired tab shows actions that were scheduled to be executed, but for which the corresponding queued commands were not executed within the expiration limit. By default, any command that gets scheduled and entered in the MSMQ has a 15-minute expiration time. So if a command is scheduled to execute at 5:00pm and the command has not been executed by 5:15, the MSMQ system will automatically mark that command as expired and move it to the MSMQ dead letter queue.
This functionality prevents old commands from getting executed at a time that is no longer is valid.
The most common reason for an expired command is a problem with the command queue server or a stopped windows service. Anytime the command queue windows service (Events2HVAC_Service) is stopped either by a failure, manually by a user, or if the PC hosting the command queue server is shutdown, there will be potential for command expiration.