L/R power balance displayed during rides is incorrect on Stages SB20

App (iOS on iPad) reads right pedal power as 100 and left as 0 during rides on Stages SB20. Both power meters have brand new batteries and fresh calibration (zero reset) did not change the app behavior. Nor did restarting the app or the device. Power meters are sending correct data, because the Stages app reads credible values for L and R power. In “connect devices” dialog in FulGaz, I see a nonzero power reading for the L pedal while pedaling, but the R pedal shows steady 100.