I have posted about this before on Zwift and TrainerRoad. For me it was the garage door which caused sunlight problems. I’d be spinning away and someone would open the garage door thereby flooding the kicker with sunlight.- speed and watts would go haywire. What made it worse is that sometimes it didn’t recover immediately once back in shade. This made me wonder about other possible causes (RF, temp) so I’ve been troubleshooting all summer. I even received a new PC board from wahoo after a spin down reported a temp way out of range - but possibly also due to sun?
I tried a cardboard wheel box to shade it but that only worked sometimes- causing more confusion.
But, sun is definitely the culprit. It doesn’t have to be direct sunlight (which is why the box wouldn’t always work). Our eyes have amazing dynamic range but it’s seems the light sensor which the KICKR uses to measure speed does not. It also appears that the sensor calibrates itself when you start spinning to but a sudden change in ambient light messes with it. This would explain why putting it back in shade didn’t immediately remedy the problem, at least not always.
It made me wonder why wahoo used an optical system to measure RPM/speed? It may be because the resistance unit is right there and creates a strong magnetic field so a magnetic cadence sensor would not work.
My solution was to move the KICKR so it never gets direct sunlight. A more sophisticated shroud would be needed as a permanent solution if you want to workout and get a tan at the same time.