I’m using a KICKR Snap, using BLE/mobile app, running Zwift on my computer. During the FTP test or during a workout, when the workout calls for going from high to low wattage, as I slow down my pedalling to put out less power, the resistance will start to increase, despite my still being above the power target. If I slow down further, resistance increases even more, until I can’t pedal. Same thing happens if I shift to a lower gear. I wind up having to stop, let it drop temporarily out of ERG mode, then try starting again (successful about 50% of the time). Could this be interference with the BLE signal? When at a constant cadence/power section of the workout, measured power can be +/- 20 or 25w even with steady cadence.
You shouldn’t be shifting gears during workouts. Are you choosing a neutral gearing for your chain? Have you also done an FTP test before doing any workout program on Zwift?
If you have not already, check out our article about how to use ERG mode in workouts. There is a lot of good information there, as well as FAQ that might help. If you are still having issues, open up a support ticket and we can help!