Here is some of my journey with the failure of "iCloud Tabs". I suffered from "Phantom Tabs" back in Feb/March. I tried signing out of iCloud, disconnecting Safari from iCloud, restoring, etc. Nothing worked. Then, one day, iCloud Tabs stopped appearing altogether. For the past 3-4 months, I have not had any iCloud Tabs appear across devices (each device only shows its own tabs). Every device is fully up-to-date with the latest OS installs.
I have tried everything to deleting history, closing all tabs, etc. to no avail. I should note that everything else (handoff, contacts, calendars, safari bookmarks and history, etc.) works without problem. That is the frustrating thing: If I go to Safari history on my iPad, I can see everything I visited on the Mac and iPhone (and vice-versa); however, I can't see which tabs are open.
I finally called iCloud Support today. The person was very nice and walked me through the standard "log out/log in" procedure, etc. They told me that handoff is the only supported way to open a page from one device onto the other. They said that iCloud Tabs is no longer supported. I doubt that is actually the case, as the phone reps are just reading from a script and Q&A book, and we worked through trying to get it to work for nearly an hour before they said that handoff is the only way.
I've honestly moved on from iCloud Tabs since they haven't worked for months for me, but it is frustrating. Handoff is also annoying because as soon as you click the "remote Safari" icon, it disappears, so you are limited to one handoff until you leave and go back to safari on the remote device. I've taken to using airdrop for most of my handoffs (that is if airdrop sees the other device on any given day). I'm not sure at this point when or if any of these features will work.