Checking the file properties of the emails will show they are coming from both Jaspersoft servers in cluster, respectively.
The issue is related to the fact that too many reports are scheduled in the same exact moment.
Release : All Supported Clarity releases
Component : CLARITY JASPERSOFT
Make sure you don't have more than 5 reports scheduled at a time. Jaspersoft has a complicated logic on which reports get run at one time. The default settings are as below (timings may vary depending on the configuration):
There may be a need to confirm with Broadcom and Tibco Support that your configuration is appropriate. If this is the case, Tibco does not recommend increasing thread amount or any of the misfire intervals set up.