As you describe on the Raspberry Pi, I struggle with erratic notebook scrolling performance on a Mac every day. So this is not specific to the Pi. This problem has persisted over the last several major Mathematica revisions. It also seems independent of operating system upgrades on the Mac. I recently bought the fastest iMac ever, with lots of memory (32 GB), and while overall stability of Mathematica improved, the scrolling problems persist. If I open a notebook over 1MB in size, pure text, or mixed text and Graphics, containing many cells, and start scrolling, searching and opening cells, the scrolling control degrades or cursor focus is lost. The cursor may jump to unexpected places in the document, instead of moving smoothly. The Find function ceases to work right, the position of the scroll indicator gets stuck at the top or bottom. One sometimes successful fix to regain cursor focus is to change the magnification to very small, if, after a Find, there is no hilighted object visible. I have tried disabling all the nice FrontEnd formatting features to simplify the system, but have not found any remedy. Small notebooks work fine. These issues arise when the FrontEnd has to deal with >1MB sized notebooks with many cells. Anyone else experiencing scrolling issues?

(Problems seen on Mathematica 10.3, iMac 27" Retina, Late 2014, 4 GHz Intel Core i7, 32 GB Ram, 256 GB SSD, Mac OS 10.11.1, Apple Magic Bluetooth Mouse).

PS. while writing this note, I had a hunch, and disabled the standard Apple "Magic" Bluetooth Mouse on the iMac and removed the Logitech M100 mouse from my RaspberryPi2 and attached it to the iMac. Wow, the scrolling performance is now much better on the Mac .