Safari tabs sync on two macs and an iPhone does not work
It's a radical way  to solve it, but that's how I did it. Export the bookmarks.HTML  using File menu in Safari. Then start cleaning up the bookmarks, reading list and favourites from all the devices. On Macs it's easy to do using "Edit bookmarks" and right-click on an item on reading list to clear all. 


How to clear ALL items from Safari&#39;s reading list?


After all devices, and iCloud have no bookmarks, reading list etc, check the sync by adding a test bookmark. If it does, then import the HTML file. If not, try uncheck/check Safari sync in System Preferences. 

Also, this is not a verified remark, but Safari stopped syncing the moment I made bookmark folders on my Mac. I had to use them without folders.