I am using Pro version of the Backup plugin. It is configured to backup to S3 and works well when I run manual backup (this option was also available in free version of the plugin).
I have created Full Backup Schedule to S3 and set it up to ‘Every day’. After few days I can see that it doesn’t make any new backups. However when I change it to ‘Every hour’ it makes it’s work partially (database only, no files), but something works here. I haven’t tested it with ‘Every week/Every month’ option as I’d need to wait some time to find it out. But it definitely looks like the main feature is unstable.