Tacx Neo Smart Bike Power problem

I have a problem with my brand new Neo Smart Bike I think. Somehow when keeping the same gear and Cadence, the watts keep going down. And i mean ALOT. So either then i have to push harder in a higher gear to maintain that level, untill it becomes too much. Or I can see the watts go away, even when the effort on the bike stays the same. 

Anyone any ideas? In this way its very hard to keep a steady pace and cadence, i am constantly shifting gears to keep some sort of level happening. I think that is very strange behaviour.

So for example in 18th gear i go up to 200 watts with a cadence of 80 something, and then suddenly the watts start dropping to 180 and then to 160 and stick around 150, so i would have to gear up again to get back at 200 watts, but now i have to put more effort to get at 200 watts. And then same thing happens again, higher and watts start dropping..

Or maybe some setting is wrong?