AFAIK, neither UMMU or DG-IV has been updated to work with Orbiter 2016. So most likely the DG-IV spawns below the actual terrain which causes a phenomena called Z-fighting. It is when the graphics engine can't decide what to render on the top and what to render on the bottom so everything gets mashed together leading to the flickering you see. So I would advise that you use a different vessel, one that has been updated to work with the new touchdown point model used in Orbiter 2016.