ZP data doesn't match Strava

Yesterday, I raced and the live data for 5 min. power in ZP was 5.9 w/kg. Later, when the fit file was uploaded, this changed to 5.3 w/kg. I understand the difference in accuracy between these two. However, Strava indicates my power output for 5 minutes as 390 watts, which in my case is exactly 6 w/kg. Where does this difference come from? I expected the value in ZP (based on the fit file) to be equal to Strava.

Hi @_R_Klein_Team_NL, Welcome to the Zwift Forums!
Fernanda here, part of the support specialist team at Zwift.

I appreciate you use this space to share your concerns. And I know how important is the accuracy of your results. Let’s get you some one-on-one assistance. Considering we wil need to check some personal information please use the Contact Us link on Support.Zwift.com. My team will be glad to answer your questions and check the information on the Zwift Power profile to help you out!

Ride On.