Try using https://app.plex.tv/desktop.
Edit: Various stats require minimum versions of PMS & Plex Web. Server dashboard real-time RAM graph requires PMS 1.15.3 & Plex Web 3.95.1.
The version of Plex Web distributed with PMS always lags behind the hosted version at plex.tv. Depending on what version is included with your PMS, you may need to use the hosted version to see all the stats, graphs, etc.
