I am also experiencing a syncing problem, as in it isn't syncing. MacOS 10.13.6 iPhone XR with iOS 12.1.4 and iPad Air with iOS 12.1.4. I have manually synced on the iOS devices, but it does not actually sync. I am using Dropbox as the "exchange".
I'm sorry to hear you're having trouble syncing using Dropbox. Please review this guide for assistance: