Streamlink is a fork of livestreamer and currently seems to be more stable when it comes to playing ustream streams. I had it running yesterday on an RPi 3 B+ and didn't have any connection loss (read error / stream timeout) for an hour until I just closed it.

With livestreamer I wasn't able to get past a few seconds.

So basically I'm at the start again, just being able to play the HDEV stream.