Since updating to LR CC 2015.6 Lightroom frequently locks up when selecting to import photos from an iPhone or a DSLR SD card. The problem does NOT occur with every import. But when it does occur sometimes it is necessary to delete the com.adobe.Lightroom6.plist file in order to successfully import after the force quit. Other times it is NOT necessary to delete the prefs file in order to do the import following a force quit. iMac 27", 8GB RAM, OS X 10.11.5, about 1TB free disk space. Is this a LR bug in the latest version? Didn't happen with previous versions.
I have the same hang an import in LR 6.6, El Capitan running. I have to kill LR every time, then the restart takes forever and usually the import works normally on the second attempt. Using Apple's Photos app, all works normal. I never had an issue like that before LR Version 6.6.
We have released an update just now to fix the issue: http://blogs.adobe.com/lightroomjournal/2016/07/lightroom-cc-2015-6-1-now-available.html