Finish time difference

This may have been answered before but why is there a difference in race result times between Zwift and Zwift power. Seems off by about 30 secs.

Actually the Zwift time at the end of ride was 30 sec faster than the Zwift power time.

zwiftpower counts the time from the gun/start.
Zwift counts the time from the start line only.
Usually in events, you will go 20 seconds or so before the timer on the top of the screen starts.
Strava does not catch those first few seconds either. I’ve done tests and proven it.