Since upgrading to macOS Sierra I haven’t been able to complete a time machine backup on my MacBook Air, though until now I hadn’t known what the reason might be. A search on my trusty pal Google revealed other users of Sophos anti-virus were similarly facing the same problem, users spraying their forums with complaints. It would seem that by disabling Sophos time machine backups manage to complete, something Sophos themselves acknowledge on their forums.
I gave this a try today before heading off on my next (short) holiday, and sure enough, the second I disabled it the backup got underway and progressed as expected. It’s a tad frustrating to have to disable something that’s meant to be protecting your machine, hopefully 10.12.1 will bring with it solutions as Sophos seems quiet at their end.