You have created custom notification messages for your Symantec Endpoint Protection (SEP) policies. However, on computers running Windows 10, the custom message does not appear in the pop-up notification.
Windows 10 displays notifications as toast notifications by default, instead of the previous default of balloon notifications. These toast notifications are limited to a certain number of lines, so longer messages with new lines within the message may not display in full.
You can change the default behavior for Windows 10 toast notifications using a Group Policy Object (GPO). You can find the group policy to modify in the following location: User Configuration > Administrative Templates > Start Menu and Taskbar > Disable showing balloon notifications as toasts.