The DSMs produced from images from my Mavic Air are always in the negative by a few tens of meters.
These used to be processed on Pix4D cloud. My first time to process on Pix4D mapper, the same thing happens. However, the Mapper shows you more things and I noticed that it was incorrectly reading the image metadata. On the file itself, the altitude is correct (50 meters), but when imported for processing, the software reads it all as 1.2 meters. See image below.
So when the data set is processed, negative surface elevations will be the result. The bandaid solution is to manually correct the altitude on mapper before it starts processing, but this is only feasible for a small data set and not for data with hundreds of images. How can this be corrected automatically?