SOLVED: Can't see other clients in the "cast to" devices list

[auxym]

I'm not sure what changed recenetly, this used to work 1-2 weeks ago. I have not upgraded my JF server, but the clients (Jellyfin Media Player) might have been, I'm not sure (rolling release distros, I update everything frequently).

• Two instances of Jellyfin Media Player on Linux (one on EndeavourOS, the other is OpenSUSE Tumbleweed)
  
• One is running 1.12.0, the other still on 1.11.1
  
• Both connected to the same JF server (v10.10.6) running in Docker on Truenas, on the same LAN.
  
• I used to be able to click the "Cast To" button in either client, see the other one and being able to cast to it, or remote control
  
• Now, when I click "Cast to" in either client, the list has only two entries: this device, and Google Cast. For what it's worth, casting to my gen2 Chromecast works great.
  
• I have also tried other clients: the web one and Jellyfin Android on a phone, and none of them can see other clients or are seen by it.
  
• The clients do appear in the admin dashboard Devices page
  

Searching led me to this thread: https://forum.jellyfin.org/t-cast-button...light=cast but it concludes that the DLNA plugin is it culprit. I do not have the DLNA plugin installed on the server.

I can try searching logs, but I'm not sure what to look for. Also server logs or JMP logs?