My Zwift will suddenly keep telling me I’m going at a rate of many hundreds of watts when I’m only lightly pedalling?
We’ll need a lot more information about your setup if you would like any assistance in troubleshooting. What trainer, what devices are in use, how do you pair to Zwift, etc…
Without knowing anything about your hardware or setup, the short answer is that it might be something with the trainer/connection if you’re using a smart trainer or if you’re using a dumb trainer it might be the speed sensor or configuration of the trainer in Zwift.