I just updated my Jellyfin to 10.9.2 and am suddenly having this issue as well. :/
Update: It's now sometimes working on the same PC that the server is running on after refreshing the guide data, but I'm getting "Playback failed due to a fatal player error" on another PC, and nothin' on any other devices.
Another update: it seems to be working fine with Channels DVR, so this definitely appears to be a Jellyfin issue.
Even more strange: the Jellyfin Android TV app appears to work fine on an Android device, but not the regular Jellyfin app. What the...