Did Apple kill iCloud Keychain wifi password sync?
I bumped into this question when searching for the problem. 

And I figured out iCloud didn't set up (or logged in) on my Mac OS X. When I logged in to icloud, KeyChain access created a new tab for iCloud just under the Login tab. 

Please be sure, you set up iCloud on your Mac OS X.

https://support.apple.com/en-us/HT208682