Yesterday I raced the British Cycling Time Trial Series at 14:40. Zwift app reported my average power as 146 watts. ZwiftPower reported my average power as 150 watts. Why the difference? (Note that my 20 minute power (152 watts) was reported the same for both.)
I assume probably because your Zwift app figure of 146w is the average of your whole ride time including the short time after you crossed the finish line, took power off the pedals, coasted to a stop and ended your ride.
The new Results screen figure and ZwiftPower figure should be a much closer figure, 150w, as both are calculated using only the actual race time.