I use Mma notebooks to present in the classroom, so for me this is a serious problem. Before starting a class, I close all the sections, subsections, and subsubsections. During a lecture, I open these and close them back down as I move through the notebook. I will be merrily moving through my notebook, when suddenly I can no longer scroll. (Both the scroll keys and the scroll bar stop working.) I have had this problem occasionally in past versions, but I seem to be seeing it more than every in 10.2. Is it worse, or have I just become unlucky?
I think the problem occurs most often when I open a closed subsection. I can sometimes fix the problem by reducing the notebook magnification. (My recollection is that reducing it to 100% used to be a nearly sure-fire fix, but this no longer seems to be the case; sometimes even lower magnifications do the trick.) Sometimes this change in magnification fixes things: I can even restore the magnification, and continue to scroll. Other times, I have to close the "offending" subsection, and if I am lucky, I can reopen it and continue to scroll. In the worst case, I cannot scroll with the subsection open, forcing me to either close Mma and reopen it (usually works) or skip prepared material. I would appreciate hints/clues for how to deal with this situation in real time when it arises.