It sounds like that particular client isn't able to establish a socket connection, which is what allow you to control it from the dashboard. Do you have a reverse proxy setup for the server?
Jellyfin 10.10.3 (Docker)
Ubuntu 24.04 LTS
Intel i3 12100
Intel Arc A380
OS drive - SK Hynix P41 1TB
Storage
3x WD Red Pro 6TB CMR in RAIDZ1 (JF Library)