Can't connect to selected server

[SenileOtaku]

Just today this started happening on my Jellyfin server. 

Jellyfin 1.9.8
Fedora 40 (baremetal, no containers or VM)

Failing from two machines (also running Fedora 40) with Firefox 129, Chromium 127.0.6533.99, and jellyfin-media-player 1.10.0-1.
Also failing on a Mint 22.04 system (Firefox 129)


Even trying from the Falkon browser on Haiku, connecting to http://192.168.3.15:8096, it shows the "Manual Login" option (on the "Please Sign In" screen), but logging in with that just drops me right back to the Please Sign In screen that only shows "Manual Login" and "Forgot Password"

I've checked the ports on the media server:

jelabarre@5040mediaserver:~$ sudo ss -tulpn | grep jellyfin
udp  UNCONN 0      0                              192.168.3.15:48054      0.0.0.0:*    users:(("jellyfin",pid=1036,fd=482))   
udp  UNCONN 0      0                                    0.0.0.0:7359      0.0.0.0:*    users:(("jellyfin",pid=1036,fd=485))   
udp  UNCONN 0      0                            239.255.255.250:1900      0.0.0.0:*    users:(("jellyfin",pid=1036,fd=481))   
tcp  LISTEN 0      512                                        *:8096            *:*    users:(("jellyfin",pid=1036,fd=514))   

jelabarre@5040mediaserver:~$ sudo lsof -i -P -n | grep jellyfin
jellyfin  1036        jellyfin  481u  IPv4  10186      0t0  UDP 239.255.255.250:1900
jellyfin  1036        jellyfin  482u  IPv4  10187      0t0  UDP 192.168.3.15:48054
jellyfin  1036        jellyfin  485u  IPv4  10188      0t0  UDP *:7359
jellyfin  1036        jellyfin  514u  IPv6  10193      0t0  TCP *:8096 (LISTEN)