Ok the did all the above - and the error returned... but a quicker fix for me was - when the sync error happens, and it wants you to resolve it by entering a new password - which no matter what you put in - it will say is incorrect. Then I press continue - and it will ask you if you want to overwrite the dB on OneDrive. I say yes - and it all syncs. Then when I go to my other devices, they have resolved themselves. Note - when you do select continue - it will show the last time the password was changed - and (in my case) it was showing a date and time that I know I wasn't using that device. So not sure if that was an error - or is it triggering something else.
I suspect this will happen again tomorrow - and if does I will update things here.