Why do I have to login to plex.tv when locally accessing plex PMS?

Hi there

I use PLEX PMS (latest) on Mac OS X El Capitan.
Works grand for years (mostly)

Now suddenly, I am forced to login to plex.tv each time, when I open PMS locally in a browser
http://127.0.0.1:32400/web/index.html#
Emptying cache & all that did not help, neither did adding local IPs to the no authentification option.

I read plenty of posts on that issue, but there was no real solution I found within the forums.

Really would love to be able to just use my PIN locally again, and not have to sign in via plex.tv

Help is appreciated