A Microsoft file hosting and synchronization service.
David IOW - thanks for this - in parallel with you I'd tried making a copy of the exe file and copying it back post delete - and that seems to restore it... although as other posters say, it then needs a big synch.. and produces errors and duplicates.
You don't say if you're running Malwarebytes - so far this is feeling like a common factor from other posters...?
Thanks
M