Came to post this as well, as my normal pc I watch plex on through the web client isn’t working. Just getting a page took too long to respond error. Another pc I’ve never connected to, redirected to the app-qa.plex.tv link and wanted a sign in.
The plex status site shows no issues with plex though, is that inaccurate?
I had an issue connecting about 10 minutes ago. I noticed it had redirected to 8080 port as well. Using my bookmark https://app.plex.tv/desktop it fails to load. When I remove the “desktop” part of the link, it immediately loads, and redirects to https://app.plex.tv/desktop/#!/. Try removing everything except app.plex.tv in your browser for now.
I thought it was the shortcut for the “Home” sidebar, but it appears at the start of every single library I got. It’s probably just some HTTP flag to signal to a parser to stop/start reading the URL at that point.