Thanks for the reports.
1. It would help us a lot to have a bit more context – does this happen under a specific set of circumstances?
2. Unfortunately this is in the nature of asynchronous USB audio. USB audio devices that use synchronous mode are a lot simpler to use; you just plug them into your computer and they pretty much “just work”. The H9000, however, uses asynchronous mode, and unfortunately, that means it might need additional configuration for it to work correctly. It has to use this more complicated mode, because it supports many different audio protocols with different possible clock sources. To use USB audio on the H9000, you’ll first want to set the sample rate you want to use on the H9000 or in Emote; you can do this on the H9000 in SETUP mode on the Clock page or in Emote on the SESSIONS page on the Clock tab. Then, you’ll want to make sure that the computer is using the same sample rate. If the sample rate is or was mismatched between the H9000 and the computer, USB audio will be muted. To fix the sample rate mismatch problem, sometimes you need to switch the H9000 USB Audio device in the Audio MIDI Setup app to the wrong sample rate and then back to the right sample rate. This is described in more detail in the H9000 manual.