Hello Brent,
This is because in order to use this functionality you must acquire the mutex that wwise requires during the process of rendering audio. Trying to acquire this lock and bailing if you can't ( as I assume you doing based on what you say ) will at least avoid the contention that causing your hitches. This does however suffer from a potentially very stale value if you fail to acquire the lock for a long period of time.
Another thing to consider is that global callbacks issued by wwise are ensured to issued at a point where this lock is not under contention making the call relatively cheap, if your usage can be adapted to get the value in a global callback this might a good solution.
That being said I personally prefer using a dedicated callback. I would be happy to discuss with you how to do this over email dan@oticsoftware.com.
Best,
Dan Murray