I'm also getting the 400 error, but adding /web to the url doesn't fix it. Clients are still working it seems but no luck with the webui.
Here are the logs from a docker restart:
2025-05-05 00:10:57.301945 [info] Host is running unRAID
2025-05-05 00:10:57.323003 [info] System information: Linux Dan-Server 6.6.78-Unraid #2 SMP PREEMPT_DYNAMIC Thu Feb 20 13:33:15 PST 2025 x86_64 GNU/Linux
2025-05-05 00:10:57.343802 [info] Image tags: BASE_RELEASE_TAG=2025032801,IMAGE_RELEASE_TAG=1.41.7.9717-1-01
2025-05-05 00:10:57.369498 [info] PUID defined as '99'
2025-05-05 00:10:57.399737 [info] PGID defined as '100'
2025-05-05 00:10:57.455331 [info] UMASK defined as '000'
2025-05-05 00:10:57.477473 [info] Permissions already set for '/config'
2025-05-05 00:10:57.510878 [info] Deleting files in /tmp (non recursive)...
2025-05-05 00:10:57.535973 [info] TRANS_DIR defined as '/config/transcode'
2025-05-05 00:10:57.569452 [info] SHARED_NETWORK not defined (via -e SHARED_NETWORK), defaulting to 'no'
2025-05-05 00:10:57.590391 [info] Starting Supervisor...
2025-05-05 00:10:57,864 INFO Included extra file "/etc/supervisor/conf.d/plexmediaserver.conf" during parsing
2025-05-05 00:10:57,864 INFO Set uid to user 0 succeeded
2025-05-05 00:10:57,866 INFO supervisord started with pid 7
2025-05-05 00:10:58,868 INFO spawned: 'plexmediaserver' with pid 64
2025-05-05 00:10:58,869 INFO reaped unknown pid 8 (exit status 0)
2025-05-05 00:10:58,972 DEBG 'plexmediaserver' stderr output:
Plex Media Server is already running. Will not start...
2025-05-05 00:10:58,980 DEBG fd 8 closed, stopped monitoring <POutputDispatcher at 22646628284944 for <Subprocess at 22646628284608 with name plexmediaserver in state STARTING> (stdout)>
2025-05-05 00:10:58,980 DEBG fd 10 closed, stopped monitoring <POutputDispatcher at 22646626747728 for <Subprocess at 22646628284608 with name plexmediaserver in state STARTING> (stderr)>
2025-05-05 00:10:58,980 WARN exited: plexmediaserver (exit status 1; not expected)
2025-05-05 00:10:58,980 DEBG received SIGCHLD indicating a child quit
2025-05-05 00:10:59,984 INFO spawned: 'plexmediaserver' with pid 70
2025-05-05 00:11:00,986 INFO success: plexmediaserver entered RUNNING state, process has stayed up for > than 1 seconds (startsecs)
2025-05-05 00:11:13,418 DEBG 'plexmediaserver' stdout output:
Critical: libusb_init failed