@Nate_Pearson thanks, and yup that was the ride back in March that had dropout issues and delayed start to a few intervals.
The problem - I had the ANT+ adapter plugged into the side of my MacBook Pro, sitting on a metal table next to my trainer in the garage. The battery on Stages was fine.
The fix - putting the ANT+ adapter at the end of a USB extension cable, and hanging near crank.
The ultimate fix - switched to running TR app on my iPhone, because I stopped paying for Zwift and didn’t need ANT+ anymore.