I've set up the new Photos app, first on my Mac Mini where it successfully uploaded all my iPhoto photos and downloaded my iOS photos. Second, I've set it up on my Macbook Pro where it's now stuck! There are 2979 items left to download of about 7000. Every time I close and re-open the app a couple more are downloaded. But that's a lot of closing and re-opening to finish downloading all the items! I've tried "pausing" and resuming the downloading of the iCloud Photo Library. I've also tried rebooting a couple of times. Any suggestions how I can get it to get going again?