So there are a good amount of posts regarding this issue but I believe I have implemented the shutdown process according to that advice and I am still getting the error. Also, the only post with this particular code appears to be rather old and related to the Lumberyard Engine itself (We are using UE4).
In my shutdown server process function, I am first calling TerminateGameSession, then checking that the outcome was successful, then calling ProcessEnding and again om a successful outcome then and only then do I call FGenericPlatformMisc::RequestExit(false); which tells Unreal to cleanly shutdown.
I am getting no obvious errors in the game log, it looks like it is shutting down cleanly.
I even inserted a 5-second sleep after both successful outcomes and still get the error.
Any help would be appreciated. Thanks!