Resistance does not follow gradient (SIM) / Kickr Core, Mac

Resistance seems to be quite random - the road starts going downhill (-2%), but suddenly there is a lot of resistance and my Kickr Climbs shows uphill 6%… This problem appeared around a week ago, after the new release of Zwift. Downgraded the firmware of my Kickr Core to 1.1.1, but nothing has changed. When I change the resistance manually while doing a training on the Wahoo app, the trainer responds immediately and as expected.

Any solutions for that problem? It drives me mad. I wish I could not give a damn to Makuri islands and start using the properly working Zwift again…