I understand that the asymmetry of the radiation characteristics (in both planes) is doubtful. I think that the measurement results are correct, but the antenna is asymmetrical in both planes (for example, different screen dimensions).
There is some doubt that the width of the beam is the same in both planes (they should be different, wider in the H plane, narrower in the E plane). I assume that the antenna is a single radiator (because of value of gain)