I don't want to start a new post, so I will add more to this one.
The cross-device sync is not working for me too. I am adding websites to reading list on my iPhone, and they don't show up on iPad. The same applies to favorites tabs, none of the changes I made on my iPhone syncs to iPad.
I tried troubleshooting - which is, disabling and enabling back the sync - it does not help at all (I tried disabling on both devices, then enabling on iPhone first and then iPad).
I even tried to delete Orion on iPad completely - and - it pulled in some iCloud data, but the things it synced on new install are all the same as I had minutes before THE iPad. So, it looks like it just loaded back what was there stored for the iPad (not sure if this was from local storage, even after the removal of the app, or from the cloud) instead of pulling in what I would need - the data from the iPhone.
I wouldn't blame iCloud itself here, because I have dozens of apps with much more data than just tabs and reading lists, and they all sync seamlessly between my iPhone and iPad using the iCloud, I believe there's something more to it than to just blame Apple cloud.