During a couple of my rides, after a few minutes of pedaling, I noticed that the power reported by Zwift was different from the power reported on my SRM PC7. Each time, I realized I had not done a zero offset, I just started riding. So I stopped pedaling (which correctly caused my Zwift power to go to zero and my avatar to pull over and stop), then did a zero offset on my PC7, then started riding again. My avatar just sat there and the Zwift power showed 0 even though my PC7 showed 250w. After 10-20 seconds, Zwift started showing 10-30 watts and my avatar kind of started, then pulled over and stopped, then kind of started, but stopped, and this repeated this several times. After 2-3 minutes of my riding at 200-250w, Zwift started accurately showing power and my avatar started going again and everything returned to normal.
I’ve had the same experience multiple times. It appears there is an issue with Zwift paying attention to power signals if the rider stops for 30s to a minute and then restarts.