Snapshot will not run on schedule

On my site at and I'm currently having an issue where I have backups scheduled to run automatically and despite getting traffic on my site daily the scheduled backups *never* run unless I actually go into edit and select run immediately and then save things.

I tried this with local, SFTP and Dropbox (all authenticated and ready to go) and none of them will run. Additionally even if I save immediately the files will not be pushed to Dropbox or the external server.

Thanks very much in advance,