After upgrading to MacOS High Sierra, the preview window in TeXShop no longer updates the PDF output after typesetting.
I edit the LaTeX file in a separate (terminal) window using vim (after 30 years it's built into my fingers, so it's easier) and then use TeXShop to run (pdf)latex and display the result. Until I upgraded from Sierra to High Sierra it always worked fine: edit, click "typeset", and see the updated PDF in the preview window immediately. Now it just freezes after typesetting: the page previously visible doesn't update and no longer scrolls--it's just dead. The only workaround I've found is to kill the preview window and reopen it.
I'm running TeXShop 3.97. I get the same behavior for all LaTeX files (no no unusual packages, nothing fancy--even a single page with just text hangs up). This worked fine for many years until the High Sierra update.