Are you using the Neo’s power reading or a PM with Powermatch?
My Neo2T tracks the intervals perfectly but when I power match a Stages PM there is no way I could keep it within a watt, I’ve not seen anyone control their power that smoothly, hats off to you if you can though.
I use Zwift and Trainerroad all the time, just pair the trainer via BT to TR and either the trainer or Stages to Zwift but uncheck the controllable trainer box or both Apps will fight for control.