I’m posting this in case someone else is fighting with the thing I just spent a week on.
If you have jibri on a separate host than your videobridge, and you’re accessing it over your private LAN instead of the public internet: make sure you have the JVB UDP port 10000 open for the jibri server to access. Otherwise you’ll get the dreaded “no media received” 30 second timeout error.
I had to sit back and really think about the flow of communication before I could solve it. When I realised that the recorder user is logging into the session as an actual, but hidden, user, it clicked. If you’re not opening all UDP on your private LAN (which I refuse to do) and haven’t opened port 10000, it croaks.