This is a common problem that pops up alot for me. I will go to either drag an item or brush across the map or just simply draw a brush. For some reason sometimes I can draw out a box very quickly the drag will be fast and others its super slow or I can't drag any further than I can see in the 2D view. I will have to scroll out then drag and scroll back in. Is there a hot key I am hitting on accident causing this to happen? It is very time consuming and in convieniant.