Has anybody figured out the SESSION ERROR problem? I am another of those affected by this.
I can log in the initial front end page, but only if I use my external domain name. It won't work if I refer to the site using the IP address. It also fails when I try to connect to the admin page, either using IP address or domain name.
I think that it is probably related to my LetsEncrypt proxy configuration, but I don't understand why it broke at the last update. It worked fine until then.
I looked at the link kindly provided by aptalca, but none of the suggested issues seem to belong to my configuration. I already had default and admin locations in my proxy configuration.