There has been an issue reported in using Mathematica 32 bit on the Mac. This particular use case is using a Macbook Pro (Retina, 15 inch, late 2013).
The application hangs (sometimes) during the following:
1. Using the laptop with an external monitor in clamshell mode (laptop closed, monitor on);
2. Disconnecting the monitor from the laptop which causes the laptop to sleep;
3. Waking the laptop from sleep without the monitor.
or in the reverse order:
1. After using the laptop, sleep the laptop by closing it;
2. Connect the laptop to a monitor and keyboard;
3. Wake the laptop by pressing a key on the (attached) keyboard, leaving the laptop in clamshell mode.
4. A reinstall of Mathematica has not resolved the issue.
Wolfram statement: (as of Oct 5, 2017):
We have seen this problem and are working to solve it. Currently the Mathematica front end is a 32bit program and and that is contributing to the problem. It is not unique to Mathematica but seems to be related to the 32bit application. We are working to fix it but I am not sure at this point when that will happen. Hopefully in the next release but that has not be set yet.
IS&T will stay in touch with Wolfram to obtain a timeline on an upgrade or a patch to resolve the issue.