gray fog covers the orthomosaic map

Hello. I am using a drone DJI Phantom 4 Multispectral and Pix4DFields for agriculture
investigations. Yesterday after processing of photogrammetry of Pix4DFields a strange gray fog covers the orthomosaic map and although the weather was clear and sunny during the flight. And also the NDVI histogram calculated after the mapping looked strange. Does anybody has any idea what could cause this artefact?
Thanks in advance for your help.

Hi Norbert,
Did you use full blending under advanced features as it can improve color transitions. Furthermore, did you select Clear sky for the weather conditions? This will ensure the correct radiometric correction is performed.