Rough pedalling at high resistance?

I’ve just managed to buy a new Neo 2T as a replacement for a Tacx Flow I’ve been using.

Overall it’s really impressive but I’m experiencing one thing that surprises me – at very high resistance and relatively low power, say for example on a 10%+ gradient when the app is simulating 100% difficulty, the pedalling gets really rough and lumpy. All other times it’s nice and smooth.

Has anyone else experienced this?