Every time I had a new Canary build, I went to my iPhone. Stopped syncing (it wasn't working anyway), deleted all synced favourites and then restarted the syncing process. Yesterday, for the first time since the bug syncing process was brought up, I got a complete sync of my favourites.
The problem being fixed for me doesn't mean it's fixed for everybody. What's more, even if it turns out the problem is fixed for some iPhones, it doesn't mean it's fixed for all smartphones.
Which brings me to my point. What if all those with syncing problems try the following:
1- Turn off syncing on your smartphone
2- Delete all favourites
3- Start syncing again
4- Wait about an hour then report here to let Microsoft know if the problem is finally fixed