iPhone Sync Still Fails to Start in iTunes

iPhone SE running iOS 12.0.1

iMac running Mac OS 10.13.6 and iTunes 12.6.2.20

When I connect the phone by cable, it shows up in iTunes. When I hit "Sync", it tries to start syncing but the sync never starts - I get the message: "The iPhone could not be synced because the session failed to start"

I'm syncing / backing up to the Mac - not to iCloud. Also, I rebooted the Mac and the iPhone - no help. The iPhone won’t sync to the computer in iTunes whether I use the Lightning cable or trying to sync over WiFi.

The iPhone synced fine prior to the iOS 12 update. This is my first attempt at syncing running iOS 12. I have an iPad Air 2 running iOS 12 and it syncs fine on the same Mac / same iTunes.

I fixed this problem by re-starting the iMac in Safe Mode, then re-starting the iMac in normal mode, but a few days later, when I again tried to sync the iPhone, and the sync failed to start again.