How to sync my macbook and iPhone calendars after this stopped working with the 10.11.5 OS X software update

Do any iCloud features work?

Verify that you are signed into iCloud on the Mac. Try signing out and then back in

Try going to iCloud.com to see if the items are there and whether they are from the device or the computer. That should show whether the device or the computer isn't syncing. If the computer, try going to System Preferences/iCloud and stop syncing. Wait a couple of minutes, then recheck syncing. If the device, go to Settings/iCloud and do the above. You can also try signing out of iCloud and then sign in again.