When trying to export the total number of agents that a DLP system has in DLP (versions 12.5 - 14.0.1) to a file from the Agent Summary Report in the Enforce console the default limit is set 30000.
On the Enforce server (Windows) go to the X:SymantecDLP\Protect\config\manager.properties file or (Linux) /opt/SymantecDLP/Protect/config/manager.properties and edit the following value:
# The maximum number of Agents than can be allowed to export, print or mail from Agents Summary Report or Agents Legacy Summary Report.
com.vontu.manager.advanced.summary.export_or_print_or_mail.maxrows = 30000
Before attempting to change this value make sure to either make a copy of the default setting or the manager.properties file in case you need to rollback for any reason.
Change the 30000 value to a value that will reflect accurately the total number of agents that exist within the DLP system. Example - 40000.
After making the change save the file and restart the DLP services as per - https://support.symantec.com/en_US/article.TECH220062.html
You will now be able to export a report of 40000 agents successfully.