I continue to have issues with my Edge830. I downgraded tonight to 8.10 so will report on how that helps or not shortly.
One thing I did seem to see in an experiment was that if I put the sensors in my hand and held them right next to the Edge830 head unit, then the drop-outs seemed to stop. Not sure what that could mean unless Garmin did something to ANT+ interfacing with the firmware upgrade.