Which recent update? I guess you mean the hosted webapp update as I have Plex Media Server 1.20.3.3437 installed on my MacBook and that shows the login screen when going to the local webapp.
Guess it was Plex Media Server 1.20.4.3508 that updated the web app and has therefore opened this can of worms.
I personally was not aware of the change to the availability of the Free Content, as I am almost always logged in to the hosted web app.
ahh here it is tucked away almost as an addendum to the main release notes for Plex Web 4.36.1