P: Locks up on MacOS X 10.11.3

Lightroom CC 2015.4 locks up on my iMac running MacOS X 10.11.3. I had to force quit the application. I've tried several solutions, like uninstalling and then installing the stand-alone installer and the 6.4 updater, and uninstalling and installing LR CC2015.4 from the CC app, but nothing seems to work. The update runs fine on my MacBook Air with MacOS X 10.11.2, so I wonder if it's the combination of both updates that causes the problem.