I just installed 16.4 and it started OctaneServer automatically. It was much nicer with 16.3 which didn't, because when I kill OctaneServer it doesn't release the license. Currently on the Otoy license server my licenses are stated to be activated even though OctaneServer and the plugin is not running.
I have been having a lot of licensing issues lately, where I have to keep logging in every time I run OctaneServer. It would remember my login before. I know that when a new version is installed I have to re-login, that's not a problem for me. It's when I have to keep logging in every time I run Octane. I also haven't been switching between versions and have just been using version 4.