Snapshots not auto backing up as per schedule

I've got Snapshots configured on a stand alone site. I've scheduled it to backup once daily but it's not working. Works fine if I manually run the backup but the scheduled time comes and goes without the backup file being created.

I've checked the settings and they're identical to settings I use on another site and just can't work this one out.

Happy to grant support access if you'd like to take a look for me.

Many thanks