Question: Photos app asks to sync already-synced pictures after upgrading to iOS 11
I don't use iCloud photo library. I manually sync the photos from my iPhone 6S to the Photos app on my Macbook every few weeks using the USB connector.
A day before upgrading to iOS 11, I synced all my iPhone pictures to the Macbook. There is no New Items left on the Import tab.
Today when I plugged in my iPhone, it said I have over "800 New Items". However, when I looked closer at these "New Items", apparently they are all old pictures from 2015-2017 that I had already synced to my Macbook. Only 24 items are real, new items that I took after my last sync, after the iOS 11 upgrade.
So it seems that the Photos app on my Macbook forgot that it had synced the 800 old pictures from my iPhone. What is going on? How do I fix this?
MacBook Pro (13-inch Late 2011), macOS Sierra (10.12.6)