I have been off Zwift for a few years. I used a “wheel on” Kinetic trainer. I just bought a Kickr Core 2 with the Zwift hub. I have done a few group rides and it’s been great. I did the 2x2 30 min workout this morning and it darn near killed me. When it went from 300w to 335w, the trainer almost came to a standstill. It was like someone had put a stick in the spokes (if there was a wheel 
). I almost couldn’t get the pedals to turn even standing on them. When the 60 seconds had passed, it freed up and I was able to pedal again. I did abandon the workout. I was able to complete this same workout before years ago when using the wheel on trainer. I’m wondering if there’s something I should check in the software. Help?
Hi there. You have experienced the “spiral of death” that happens when your cadence drops too low and the trainer compensates by adding more resistance to meet the wattage target. The lower your cadence the harder it is to pedal. Keeping a smooth comfortable cadence will prevent this.
Also, you probably went from a highly inaccurate wheel on trainer to a much more accurate one. I would also suggest performing a new FTP test with the new trainer to set realistic power targets.
In addition to what Mike has already said, you should definitely check to see if there is an available firmware update for the trainer.
Thanks. That makes some sense. I probably should have started with a new FTP calc. Or an easier workout. Or both.