I believe I encountered similar issues after I fully switched to Orion and imported all my Safari data.
Specifically, I started with Orion on iOS for a week (?) or so, then added Orion on Mac and imported my data, then facepalmed for a while since it seemed like my starting on mobile had screwed up the sync with my old tabs, etc.
Tried all the suggested solutions, dove into trying to get iCloud working, finding the actual iCloud sync files after creating “ghost” iPhones by deleting the app… and then, for no apparent reason, the sync worked and it’s worked pretty well since.
So, long non-story short, iCloud syncing is dodgy and magically works or fails to work despite all your best efforts to fix it.
(I’ve had similar issues on Safari in the past, too.)
(Maybe it could be worth adding a more manual / force Orion sync someday?)