Computerworld - https://www.computerworld.com/article/2916476/apple-ios/how-to-fix-icloud-sync-in-seconds.html#tk.rss_all
iCloud sync is usually reliable, but sometimes you’ll find contacts, calendar events or other content fails to sync between all your devices in the few seconds it should take. If this seems to be happening to you, these simple tricks can help get things running smoothly again.
Is everything up-to-date?
First, check to make sure you are running the latest version of macOS on your Mac, iOS on your iPad or iPhone, or Windows on a PC.
Check that iCloud is working
It also makes sense to double-check that iCloud services are working correctly before running through any other changes. You can