It fixed my issue. My suspicion is somewhere in the iCloud database a lock was initiated. Removing the device from the account unlocked it and allowed the tabs to clear. I did this yesterday and haven't had the issue return since.I wouldn’t waste your time. So many people have done all this accounts messing about and at best it’s only a short-term fix.
The only thing I can't remember is when the phantom tabs disappeared and how exactly. Did removing the device delete the tabs automatically, or did I explicitly close the tabs while the device was no longer on my account?!?