Same problem for me with Tacx Vortex + Favero Assioma
Here´s the answer, they refuse to admit the issue
Thanks for reaching out to Zwift Support with this question!
I recommend pairing under power meter first, under power source. Then pair your cadence under controllable with your vortex.
I would also like you to try calibrating your trainer to see if this fixes the problem. Instructions are provided on our knowledge base in the article “Pairing Elite Trainers.” Please see the section titled “Calibrating your Elite Trainer.”
If this doesn’t fix the problem, please contact Elite to make sure that you have the latest firmware version for your trainer. Please let them know what’s happening, so they can check to see if there’s an issue with your trainer. Should you need to update your firmware version, it’s a good idea to calibrate your trainer again after doing so.
Once you’re ready to pair your trainer to Zwift, make sure you’ve disconnected from any third-party apps that could be stealing your trainer’s signal from Zwift and complete the pairing from the “Paired Devices” screen in-game. We’ve provided a video here.
Please give these steps a try, and let us know how it goes.
Member Experience Agent