I have a wahoo kickr power trainer. I also have a Garmin edge power pedal.
When I use zwift, the watts are constantly 70 watts lower than garmin or what I see on the kickr on wahoo app.
I calibrated both through the wahoo app and zwift but didn’t fix the problem.
Note, I was using structured workout from TrainingPeaks but it used to be fine in the past.
Only change is that I’m now using zwift on my iPad rather than Apple TV.