Resistance on TACX Flux 2 opposite as what is shown on Zwift

Hi,
yesterday I encountered a weird problem. I was riding for about 15K and everything was OK. Suddenly, Zwift was showing 0% hill and my TACX Flux 2 went on full resistance. When I went uphill, when hills were 3-4%, not much or no resistance.

I was on the France RGV route and I was wondering if the close gap between 0% and 4% repeatedly could cause that problem. My son used it today and he said that after 15K the same thing happened.

Also, at the end of the ride, I could not see my power graph. Is this related to the Zwift power update I see in this forum ?

Thank you very much for your help.

Claude Milot