Try this procedure: You need to reclaim your server, but don't dare to touch the Windows Registry
Additionally, go into your Plex data folder, into the subfolder Cache and delete the file cert-v2.p12.
Make sure that your home network is using an IP range that is explicitly assigned to “private” use. Private network - Wikipedia
Take care of a misfiring “DNS rebinding protection” in your local DNS resolver/router https://support.plex.tv/articles/206225077-how-to-use-secure-server-connections#toc-4
