Vector 3 measures less power than WAHOO kickr. Can someone help? It's constantly 20W less after countless of calibration of both devices.

Meanwhile i knew a few things about kickr v5. Lots of have bad factory calibration somewhy and overreports the power (and the auto-spindown calibration cant solve it). So, 1st of all check the firmware update in Wahoo app, update it to the latest. After, tap 10x times to the "calibration" in the app, and a hidden "factory calibration" menu will be pop up. Do the factory calibration as the app says (you will receive a summary page about the result of the calibration, make a screenshot for additional info to myself) and after this factory calibration the v5 should read lower than before. If something not clear, just let me know.

As I said I had the same problem. No solution,
Then I had another problem with the pedals and they have been exchanged by Garmin (by the way: excellent customer service. Got the new one within 2 days)
Since then Wahoo Kickr and vector 3 are showing the same values.
So I guess it was a problem with the pedals and not with calibration etc...

If you want your Vector 3's to more closely mirror your Kickr power, one solution is to adjust the Vector Power Meter Scale Factor.  This can be found in the Vector settings under Sensor Details-Cycling Dynamics-Power Scale Factor.  The left and right pedal Power Meter Scale Factor can be adjusted independently if desired.  A Scale Factor of 1.000 is the default, but can be modified to anywhere between 0.9000 to 1,1000, so up to a 10% adjustment is possible.  An article on this is posted at the Garmin Support Site but note the article mentions the setting is found under sensor details, but I found it under Sensor Details-Cycling Dynamics-Power Scale Factor,, Article url:  https://support.garmin.com/en-US/?faq=dcsvFoxXte3Bmd5IMRsKb8