I recall your previous comments on the other topic about Elite virtual shifting, so it sounds like you got as far as a firmware update by talking to Elite. You may need to keep talking to Elite support but the thing I’m wondering is whether you are experiencing any Bluetooth connectivity problems when you’re seeing low speed. That could be revealed by uploading a Zwift log file to zwiftalizer.com. If power is constant then the other possibility is faulty brakes or touching the brakes on the Play or Ride controls, but I’m not sure if that’s what you have. What is the virtual shifting device you are using? If it’s Play or Ride controls, you can go into settings and move the Braking Sensitivity slider all the way to the left which would eliminate any chance that your loss of speed is related to brakes.