Just to be completely clear on this … you are saying that on the 24th April you saw the exact same anomaly for the exact same time frame on both your Davis system AND your WH3081.
If true this would tend to indicate that at least on the WH3081 WD is actually reading the correct value from the sensor and it is highly likely that since both sensors are reading almost exactly the same values there has to be an external effect coming from somewhere to cause this.
This would be extraordinary since I am not sure how any of us could explain the external effect which could cause this at least not by the sun. I suppose it could be some electrical interference but again very difficult to explain.
Stuart