I noticed the same this morning after installing the 600 update last night. I frankly haven't had time to even begin diagnosing yet. Spark behaved normally, video feed was stable and I shot some awesome footage with it, but it is a little disconcerting to get that "Aircraft Disconnected" banner. And I got it right from startup. As a result I didn't take it outside of easy visual / recovery range.
My setup is OTG to an HP Android tablet. I fly mostly manually by sick, but did put it through some tracking drills and such via the app just to see, and they worked fine. If anything (and it might just be lack of coffee this morning) the Spark seemed slightly sluggish on the throttles.