Just did a 20 FTP test and noticed a 25 watt difference between Zwift and Wahoo Fitness app. Had them running side by side and also notice Zwift was much higher that Wahoo during the effort. What one is the more correct Ha Ho?
Zwift avg power: 233
Wahoo App avg power: 208
Equip: Wahoo Kickr
FYI - Was done on a New Wahoo Kickr and spin down test was done before. 
Assuming the two use the same calculations for average power (which I’m not sure of), the only reason for a difference would be if one program was getting more/less packets than the other (i.e. your signal was dropping for one of them). Zwift doesn’t adjust your wattage, it only reads it.
You may want to start with either the ANT+ signal troubleshooting or BLE signal troubleshooting depending on which protocol you were using.
Think it could be the 2lbs weight difference?
Just checked weight setting in my profile.
Zwift 163lbs
Wahoo 165
Watts having nothing to do with weight. Were you using BLE for one and ANT+ for the other? If so I’m wondering if that could be the issue.
Ya, using ANT+ for Zwift and BLE on IPhone for Wahoo Fitness. Very strange as you would think data transfer is data transfer. Sending a number like 200 would be the same. Looks like I’ll need to do an Outside 20 FTP test to know what the real number will be for outside training. Could potentially have 3 ftp numbers. One for kickr zwift, one for inside ble wahoo and one for outside ble wahoo using Stages.
Received this from Wahoo - Don’t run 2 apps with Kickr.
Greg Gaffney (Wahoo Fitness Support)
Apr 3, 2:44 PM EDT
Hello John,
The KICKR was designed to only be controlled by one app at a time. If you’re running more than one program simultaneously, this will lead to difficulties and odd readings as these fight to control the KICKR. Our app will have more power smoothing built in to it, so your power file might not show the highs and lows. Although, the averages should be pretty close. In this situation I would imagine that something was causing some interference. I would suggest performing a spindown calibration once every few weeks. Also if using Zwift, please make sure the Fitness app is closed to ensure you are getting the correct readings.
Thanks,
Greg