My Cognitive Productivity toolkit makes heavy use of Skim, the ironically named PDF delving app for macOS. Unfortunately, however, in its release of macOS Sierra, Apple introduced major problems for third-party PDF rendering apps like Skim, problems that Apple itself somehow worked around in its Preview app (suggesting that Preview uses some non-public APIs, tsk! tsk!).
The problem causes PDF to be rendered extremely slowly, sometimes taking over a minute!, and inconsistently. I logged a bug on Skim’s Sourceforge project in December 2016.