Hi Kat
Wordfence only notified us last week that it needed updating so it was not updated as soon as the release was out.
We have around 7 blogs on the server, all setup the same. 5 of the blogs were updated last week and these were all failing to backup. 2 of the blogs were not updated and were backing up fine. As soon as I updated the 2 which were out of date today the backups fail on those too so I know it is something related to the last release.
Thanks
Ashley