Tacx movies - resistance issues

I am running Tacx movies on my Ipad. 

In 50% of the cases the movie will have the standard resistance (as when you are doing a flat workout) or the resistance will be incredible high (even when you are going flat or down). In other words the resistance does not match the slope. I can't find a pattern when these 50% occurs and when they do not. When doing the workout or the GPS, resistance match the slopes.

I have tried to unplug power, going out of the app and back in +++ but nothing seems to help. It seems as if it is pure coincidence whether the resistance matches slope.

I have checked that firmware is up to date.

Anyone facing the same issue / having a fix?