I’ve been having this same problem for the last few nights, and think I have found at least a partial solution.
We’ve recently switched to Foundry VTT - up until then, we’ve been using Fantasy Grounds (both C and U), and piping the music from an instance of the online player running on my computer through Cleanfeed. In an attempt to get better sound quality, I had everyone download the Syrinscape Online Player.
The first night we used it, 4/5 players were able to connect and hear - I just had a mood running (Witchwood), and didn’t use any of of the global one shots, since we were just getting settled into making character sheets and prepping to use Foundry. The player who couldn’t hear anything logged in after I had started the music. Everyone else already had the player running.
The next night, the same group got together. This time, only one person was able to hear. She had started up the Online Player before I had on my computer, and she was fine - she could hear the WItchwood music when I turned it on.
Everyone else in the group, couldn’t hear anything when they logged into the Online Player. I kept trying to have them reconnect, make sure their volume was up and re-register the device they were listening on.
Tonight, I got several of the players together, and set up another account and put the online player on my laptop. I had started playing Witchwood before everyone connected. The music wouldn’t come through on my laptop or on my players’ computers - I could see them connect, but they didn’t see the waveform, and did not see the graphic for Witchwood. I hit a global one shot, and everyone heard it just fine.
From there, I stopped the Witchwood music, and restarted it - and lo and behold, everyone could hear. While it was playing, I had one player disconnect and reconnect - again, the music was gone, but they could hear global one shots.
It seems that whatever call the program makes to the Master doesn’t get an answer when something like a mood is already playing. One shots come through, but the information for moods only populates and plays if I stop and restart the mood after someone joins.
Also, you must port forward port 7977, or your players may have difficulty connecting.
Is this expected behavior?
Hope it helps anyone who was having difficulty.