Not Backing Up to S3 as Configured

I have snapshot installed on three of my WP sites. All three are configured to backup to local, S3, and FTP. FTP and local appear to backup as configured (daily and hourly, respectively).

However, my S3 backup is configured on all three sites to backup all DB tables and files once daily, with a 30-day retention policy. It does not backup as configured on any of the three sites. On one, it backs up up hourly. On the other two, it appears to backup daily, but deletes the preceding backups instead of retaining the previous 29.

Deleting and re-provisioning the S3 Snapshots does not appear to correct the problem. They still behave unexpectedly, and not according to configuration.

Any thoughts?