You experience an unsollicited reboot after deploying an Endpoint Protection 14 or higher client installation package that was exported from Symantec Endpoint Protection Manager (SEPM).
Non-default client installation setting "Remove existing Symantec Endpoint Protection client software that cannot be uninstalled" may have been enabled as part of the Client Install Settings. This can be verified by opening the client installation package with a compressed file manager and verifying whether or not it includes the CleanWipe folder and the CleanWipe option is set in setup.ini, in the following fashion:
When selecting this option in the SEPM user interface, a dialog box is generated that states, among other things, that "The removal application requires a restart that you cannnot postpone or skip." This is also mentioned in the SEPM help page "About the Symantec Endpoint Protection client preinstall removal feature", referenced in the same dialog box. Hence, this is the expected behavior based on the option been having enabled in the client installation package. To prevent the reboot from happening, either disable the option that causes it, or modify setup.ini in the following fashion: