Hi Wallie. When you say photos were taken with correct exposure you mean at 0 EV? Three stops below normal is not normal [emoji16]. Please check if the Exposure Value is adequate. Sometimes it may be 0 (auto measures, not correction) but this is an average of the whole frame, and clear sky makes the terrain darker uf compensated. If the darkness is general, try to go up in exposure by some steps. If it is the ground what is dark, increasing exposure value will correct it, but will make too white the sky, thus losing blues or cloud details.
Try to look at the histogram window at the DJIGo app, and to centre the white peaks and valleys into the window frame. Also, you can upload here an example of one of your photos in order to see what can we do or recommmend.