N/A
There is an incorrect dependency in the combination with the one-time backup job if SDR is enabled.
Right click the expired backup set and click 'Show Dependent Backup Set'. The backup set has an incorrect dependencies to newer backup sets.

A hotfix is now available for this issue in the current version(s) of the product(s) mentioned. Refer to the Hotfix link under Related Articles to obtain the hotfix needed to resolve the issue.
Backup Exec 21 Update 2 - Backup Exec 21.2
WORKAROUND:
Use a regular backup job instead of a one-time backup job when the job is executed repeatedly.