My MacBook is not synchronizing to iCloud. – Looking for suggestions to fix this.
My iPad & iPhone are synchronizing Notes & contacts OK to iCloud server. All 3 are using the exact same Apple ID and password.
I can log into iCloud.com and see the notes & contacts from the iPad & iPhone. But not from the MacBook.

What I have already tried:
* Reboot MacBook
Sign out of iCloud on MacBook, Letting it delete local copies of iCloud contacts & notes.
Sign back into iCloud. Contacts & notes return.

* Syncing of notes & contacts is not working over all my devices, only the iPad, iPhone & iCloud server. But the MacBook is not syncing to iCloud. This is a fairly recent problem; about a month ago the MacBook could sync to iCloud.

MacBook is OSX 10.10.5 Yosemite

What I have NOT tried:
Erase & restore whole computer from backup. — I’m concerned that even if MacBook can sync to iCloud with a fresh, blank OSX, that once we restore all my data from back up, that this might bring back the problem too, which might end up being a lot of time spent without an actual fix.