As was stated on the first post you made about this, it's a dns or nat reflection issue.
Plex sees you accessing it through your external IP address, and not through your lan IP.
I had a similar problem, and had to roll back some nat changes I made, and now it's working fine again.
Meanwhile, free remote streaming works fine if you have a proper VPN setup. I just tested it, and was able to stream to my phone, through the Plex app, over my tailscale VPN, and I do not have Plex pass on the server or on my phone...