I have LR5 CC running on brand new MacBook Pro w 512 GB SSD.
I have a very large catalogue. (last saved was 5GB.
Very very slow backup as late as mid Nov.
At that time, when I attempt to do backup, encountered permissions issue on drive.
Switched drive, ran backup, it hung. Checked disk permissions. I have Read /Write privileges. Switched back to external drive being used. It worked.
Last night I let LR run backup overnight. Hung at 3/4 complete.
Tried running multiple times today after running Disk Utility / Repair Permissions. Turned off all apps. Checked Activity Monitor, turned off 3d party non essential utilities.