syncing across two MacOS devices

I have been using ADE for years on an iMac. I bought a new MacBook Pro and installed the product there. I authorized the product successfully on the new laptop, and it started syncing my library. There are over 50 books, ePub and some PDF. The first 12 synced fine, and then I could see the 13th book "try" to sync, and that number flickered between 12 and 13. And stopped. After that, I was able to physically transfer a file from my existing library, and add it in the app to the new machine. I also was able to download an ePub file to my new laptop, and watched it sync successfully to the older desktop. So I dont know why my new MacBook Pro can't load my full library. 

 (second semi-related issue in separate post)