I had an issue where a client was failing to back up for a period of time. Prior to the failures we had several cycles of synthetic and incremental backups.
I managed to get a Full backup through and after running incrementals for a week noticed that while the backups had all completed successfully there was an error identifying a problem with the D: file system advising to run checkdisk.
Looking at the content of the backup, via browse & restore, I found a large number of sub folders missing... which I can see if I browse the file system from the subclient properties.
The missing data is also listed if I browse / restore the earlier synthetic backups.
In the long term support will need to remediate this volume.
But, in the short term if I delete the last set of backups including the FULL that I took, and run a new synthetic will it seed from the previous cycle of synthetic / incrementals and include the missing data in the new cycle of backups?