My Logitech H800 normally works fine with Ubuntu, but sometimes, I think when I unplug and replug the USB adapter, it stops working. It is listed in sound settings under outputs, and clicking it highlights it, but sound is still played through the builtin sound hardware. Running
pactl list sinks does not show it.
My workaround is running
pactl exit, after which all works fine. I just discovered it now but I don't expect it will be a permanent fix.