I’ve got a Cycleops Fluid 2 trainer with a Bontrager Duotrap S Speed/cadence sensor connected via Bluetooth to my iPhone XS using the companion app. the sensor will pair but then go to “No Signal” and if I do get it to work, it will randomly drop out while riding requiring unpairing of the sensor and starting the pairing process over again. Tried this with brand new Wahoo Speed and Cadence sensors and get the same problem. These sensor are not paired to anything else that is on or being used. The only app running on the phone is the Zwift Companion app. there are no other Bluetooth accessories paired to the phone. Help, this is highly frustrating.
Make sure you have a strong wifi signal. There have been reports in the forums that adding a wifi extender may resolve some dropout issues.
Tonight instead of using the companion app I used the Zwift app on my phone and it worked perfectly.