Been experimenting. Did two things that may have helped. I have had no recent crashes.
Since doing the above, I have not had a single freeze. Perhaps others with the freeze problem could try these, see if it helps and let us know. Disclaimer: The below is above my "paygrade", but nobody else seems to have a fix.
1. In Users > MyUserName > Library > Preferences: In the Preferences folder, I changed permissions to so that everyone has read/write privileges. Then applied those to all enclosed items. (To open the Library, go to Finder > Option-"Go" > Library > Preferences.)
2. Before launching Lightroom, went to "Activity Monitor" > CPU > Sortup. Then find and quit "dynamiclinkmanager" if it's open. To quit, click the "dynamiclinkmanager" name, then click the "X" icon at the window top left. It looks like this should automatically launch and quit; but I'm not sure it always acts normally. Example: In Activity Monitor, I've seen four or more copies of dynamiclinkmanager open at the same time. Also, I'm not sure it's needed for Lightroom > Import. I've quit dynamiclinkmanager just before LR > Import and Import still worked OK.
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Update Jul 18, 2016: I have had much better luck by quitting "dynamiclinkmanager" just before clicking Lightroom > Import for the FIRST time and not before launching Lightroom as mentioned above. You do not have to quit "dynamiclinkmanager" again unless you relaunch Lightroom.
Trivia: When launching Lightroom, I've seen up to six copies of "dynamiclinkmanager" temporarily listed in Activity Monitor. I think Lightroom > Import doesn't "like" this copy. Thus, quit that process. Lightroom will automatically open a new "dynamiclinkmanager" when you click Import.
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(There's also a "dynamiclinkmediasever", which also should automatically launch/quit. I don't think this is a problem process.)
Trivia: I tried to downgrade LR which apparently does not have this freeze problem. But, I couldn't revert my LR Catalog to be compatible with the older version. Perhaps, there's a "trick" to do this.
Peter