You have not only the Google account, but also have a regular password on your Plex account.
Thus, you are still affected.
Go here and change your password: https://app.plex.tv/desktop/#!/settings/account
Tick the checkbox “Sign out connected devices after password change”.
Afterwards, you will need to reclaim your server in order to access it.
You can try first to use the Plex task tray icon to “open Plex” and claim the server.
If that doesn’t work, refer to this procedure: Unable to access server after password reset - #116 by OttoKerner
