The other day I changed my iCloud password. I can't remember the exact reason why I did it, but you know, you can't change your password often enough. I mean, once in a while is not a bad idea at all.
After I changed the password, iCloud suddenly started to act up on me. On desktop everything would continue as normal, but on my phone, backup started to not work correctly anymore, all of my Safari bookmarks on the phone would just disappear and some of the documents that used to synch as you would expect them to (e.g. IA Writer) would just not make it to the other device anymore. Bad days.
I read a lot of articles, all of them pretty much suggesting the same things. Quit Safari and relaunch, restart your phone, hard reset your phone or log in and log out of iCloud to make it work again. All of these tips didn't work for me.
I tried to deactivate iCloud backup and iCloud Drive, but that's when one of the major problems hits you. If you turn it off, recent changes - made it the documents that won't synch anymore - will be lost. Bad. I did save the changes of the files that I knew of to an email and then went ahead and turned it off. Data lost but that was ok, since I think it was only a few recent files that I had worked on.
What eventually worked for me, was to sign out of iCloud on all devices, to then change my password one more time on appleid.apple.com and after that reconnect all devices to iCloud, at first the MacBook and then the iPhone. This was the first time that backup would pickup synching without an error and after confirming to 'Merge all data', bookmarks and everything else started to come back again, too. IA Writer documents again synch fine as well, so I'm hopeful that this was the last time I had to troubleshoot this kind of thing.
It's been a few days now and everything seems to be back to normal. I'm crossing my fingers for things to stay that way.