The GUID of a volume could be changed due to various scenarios, such as:
1. The configured volume has been extended or shrunk.
2. The volume letter has been changed for the configured volumes.
3. The disk order has been changed after configuring the backup job.
To resolve this issue, follow these steps:
1. Check for Changes:
- Verify if the configured volume has been altered due to extensions, shrinks, or changes in volume letters.
- Ensure that the disk order remains the same as when the backup job was configured.
2. Run Additional Full Backup:
After checking the above steps, run an additional full backup for the affected job.