Based on the Lat/Long it appears you are in Belgium.
75% is probably too high a threshold for “sunny” in northern Europe at this time of year, you will almost certainly need to lower it. You can see on the screen you posted above the estimated %. Look at that value when you consider it to be “sunny” and use that as a guide.
The Davis solar sensor is a quite accurate, calibrated, device. As posted above you should have the adjustment factor set to 100, otherwise you are reducing the reading which will make the above problem worse.