Wahoo kickr core watt drop?

I have a strange problem with my kickr core. After a while of riding it seems that it drops or loses about 30 - 50 Watts.

The ride of the screenshot above was made in “another” cycling app where I rode up Mt. Teide, but I have the same issue in Zwift where I ride most. I normally happens after one and a half hour. I also had it yesterday in ToW Stage2 A … made two rides before the ToW-Ride and on Zwift KOM my the watts droped although I even put more effort in.

Does anyone has similar experience? Or hints (yeah I know, my next should be a Tacx and it will be)

if it is happening in another program then I would suggest contacting wahoo about it as it is a trainer issue