Server Version#: plexmediaserver_1.18.4.2171-ac2afe5f8_amd64.deb
Player Version#: web browser
The web interface stops displaying libraries. “On the deck”, “Recently added” and all the usual stuff is there, along with suggested content. The libraries display on other client devices. The web interface resumes displaying them when you “systemctl restart plexmediaserver”.
When it’s not working there a lot of xhr queries like https://XXX.plex.direct:32400/media/providers?X-Plex-Product=Plex%20Web&X-Plex-Version=4.12.3&… that never get a response.