Reinstalled Plex, now it won't properly start the setup anymore

I recently upgraded my Ubuntu 14.04 server to Ubuntu 16.04. Afterwards I discovered Plex did not function properly anymore so I uninstalled it using this guide.

Next I installed Plex again using the top answer in this StackOverflow question.

For some reason though the Plex setup is not triggered. When I navigate to my server it logs in using the old account (weird) and then says it cannot find any servers. The Plex web app for some reason does not understand the setup must be triggered.

Anyone knows what I can do to fix this?