Hi johan.jvr13,
Have you checked your image overlap? I can see some 'radial striping' in your DEM, which often occur in models where the image overlap is insufficient.
These blocks that are higher might be areas where you don't have enough information from images to get a proper reconstruction. For example, if they were houses or trees and you were flying at a set elevation, the image overlap on these objects that are 'sticking out' of the ground would be even lower compared to the ground. Hence, PS would not be able to model them.
To sum it up, it looks like an image overlap issue to me. Take more pictures or fly at higher elevation (reduces your resolution of your subsequent photogrammetric model though).
Regards
SAV