A job that has been scheduled to run monthly, runs automatically either weekly or on an unexpected day.
The Synthetic and Active Full backup settings under Storage>Advanced within the job run on a sub-schedule independent of when the jobs scheduler is set to run.
To resolve this issue change the sub-schedule for the Synthetic or Active fulls under Storage>Advanced within the job to have the full backup run the same day as what's set on the "Schedule" page. Disable synthetic full backup and use only Incremental with monthly active full backups.
If this is the schedule page:
This is how the Advanced settings need to look to run a single full backup once per month:
New in v8 is Forward Incremental Forever, to enable this disable the active and synthetic full option and Veeam Backup & Replication will manage the chain using the new Forward Incremental Forever method.
Please be aware that we’re making changes which will restrict access to product updates for users without an active contract.