Hi
As you can see from the image below, the power curve of Kura grows up very quickly.
At 30km/h the power should be at around 450-500W, but at 35km/h it is already at 700-800W.

So, are you sure you were at 30km/h and not a little more?
If you're sure of it, can you tell me if you feel some slipping or if you hear some strange noise?
A good test to do is this:
- do a 10 minutes warm up
- open the advanced settings in the app and select calibration
- complete the calibration procedure
- do again a training and try to keep your speed costantly at 20km/h
Please let me know the power you develop at that speed.
Regards