Attempting RDS backups with over 100 manual snapshots fails, with the following error message:
cannot create more than 100 manual snapshots
This is an AWS limitation, which allows no more than 100 snapshots of an RDS instance.
To initiate more than 100 snapshots of an RDS instance, please contact AWS support to increase the snapshot limit.
Alternatively, you may modify the backup retention policy to not exceed the 100 snapshots limit.