iCloud tabs are broken

Have tried clearing cache, history, removing all preferences, removing the iCloud tabs files in the library, turning iCloud syncing off and on, and signing in and out of iCloud. Have done this on all the Macs, have cleared history and removed Safari from sync on iOS.

Still, iCloud tabs show tabs from years ago, when I right-click to close them, they just come back.

Are they being stored somewhere in iCloud where they can't be deleted?

Until I can reset them, and until syncing works again, they're just broken. Anyone else experience this? (spoiler: you can find people complaining about this everywhere, so yes)