I've always had sync problems across devices with Windows 8, 8.1 and now 10. Most annoying one is not syncing of Web Credentials, but reading list and sometimes favorites happens too.
Let's center in last Windows 10 version, Creators Update last build, 1703 (15063.13). This happened with previous versions, but now I have all my devices with this last one. This is the last official Creators Update, updated by Today. And is not in any insider program (please, moderators, don't move this post to the insider forums because is not a question about any insider version. This happens to me since Windows 8).
Currently I have:
*Generic PC, i7 with 16GB of RAM, updated from Anniversary
*Lenovo ThinkPad W550s, updated from Anniversary
*Surface Pro 4, fresh install because update failed
*Lenovo Yoga 2 with Windows, fresh install because update failed
Once after a big update, say Anniversary, Creators and some other little updates, sync has been working for, say about 2 days. After that never worked anymore until next [big] update.
Recently I found the "Microsoft Accounts" troubleshooter and I've run in all of the machines. The common factor in all machines with this assistant is "Can't connect to the sync service". It says is my internet connection, but it is not because I'm writing this as the assistant is running and I have full internet access. Default Windows antivirus and security levels.
In this machine (the Generic PC), it says "Rootacouses found an created logs", that I don't understand what means, and "Some settings have sync turned off", that is false because all sync settings are ON. I'm almost sure they are ON.
(Please, don't redirect me to the same tutorials/pages that shows how to enable the sync options. I'm not dumb. They are enabled. In all machines. Please, please, don't. And yes, all computers are in the same account).
I really don't know what to do to resolve this. Perhaps the remote Microsoft "sync service" is down, or perhaps is down the server they assigned to me, but this is very frustrating because there isn't a easy way to find what's happening.