Strangely enough, I have all Ultra outputs (Coax, Opt, Line) connected to my Vibe, yet I've never experienced audio cutting out during playback on any input.
If this were a firmware bug, all Vibe users would likely be experiencing the same issue, but for now it seems to occur only on some users' devices. It's puzzling...
I'd like to ask you something: Does this issue occur multiple times a day?
Also, could you connect a device other than the Ultra to the Vibe to see if the same issue occurs?
(Unfortunately, I can't test this since I can't reproduce the issue on my Vibe...)