iphone sync stuck at "preparing to copy items"
I'm trying to backup my iPhone 6 to my MacBook Pro (2014) and it keep sticking at the final step and says "preparing to copy items". I tried syncing with another MacBook Pro (2012) and got the same result. I successfully synced an iPhone 5 without any problems. The software on all devices is up to date.
In addition, I changed the setting in iTunes so that the iPhone would not sync automatically. Despite this being the case, iTunes open and begins syncing each time I connect it to the MacBook. I confirmed the settings were set to prevent automatic sync. I also cannot stop the sync by clicking the "X" to stop it. I have to quit iTunes completely.