For the benefit of future IPVM searches, it appears this was resolved after adding the external address of the Event Server to the Registered Services entry in Management Client.
What happens is that the Smart Client logs in, and after authentication, the user receives the configuration required to display cameras/views/etc. The Event Server component of the software typically lives on the Management Server, and it handles alarms, maps, and other integrations like LPR, Transact, Access Control some 3rd party plugins etc. The Smart Client receives a list of registered services which are additional components that the Smart Client might need to talk to, and those can be found listed in the Management Client under Tools -> Registered Services.
If the Event Server entry only has a LAN address/hostname and the Smart Client is connecting remotely, it most likely will not be able to resolve or reach that address. So by adding an external address/port to the Event Server's registered service entry, the Smart Client will receive a more appropriate address to connect to for events/alarms/etc.