Could have been a problem on the feed provider's end.
In the future if that happens, you can use the "Report a Problem" link on the feed's page and let the provider know about it (we ask that people using that are respectful when contacting the providers)
I had a wacky sound card on one of my feeds and it would occasionally stop receiving the audio from the scanner so the encoder would be running (making the feed show as "online") but it wouldn't be getting any audio to send over the internet.