Erratic power read out from speed sensor

On my first try of Zwift in training mode I connected my Garmin speed and cadence sensor no problem via ANT+ but the power data I was given on screen was quite erratic making it very difficult to hold a consistent power.  I wasn’t using a USB extension, would this help? I kept getting “failed” notifications after each interval.  Any advice on this?

power smoothing would hopefully help with this. Three second average option or default is needed.