Please try the following steps.
Turn off the GPU from the Preferences.
Click on Lightroom
Go to Preferences
Click on the Performance tab.
Uncheck the GPU
Restart the Lightroom.
If the above steps doesn't work, Reinstall the Lightroom from the Creative Cloud.
Let us know if it helps.
Did both the GPU disable and a full re-install , both actions did NOT result in a resolution I'm afraid.
First of all, I'm not going to upgrade to El Capitan, I had too many issues with it and therefore had to restore.
Anyway, I exported all my photos as a new catalog (this ran for more then 6 hours !!! ) and used the new catalog. After this LR shutsdown normally.
So , my problem is solved.
On my Mac I'm running Adobe Lightroom CC 2015.2.1 and El Capitain and I tried unchecking GPU in the preferences, but it did not help. This is getting annoying; why don't you guys at Adobe come up with a solution that actually works?