Kenneth,
is the number the same or does it grow each day?
It could be that its just certain files that aren't being backed up for one reason or another.
What you can do is if you go to the Vault Store database that its reporting against, then open the Watchfile table.
This has a list of all the items that it is awaiting backup from, what you can then do is some random samples, check on disk that the items have had the archivebit removed and that they are on backup as well.
You can use the IgnoreArchiveBitTrigger.txt as well like gertjan says, just remember to do this *after* the backup has complete and not before, also the ignorearchivebittrigger.txt file needs to be created, not copied, otherwise this will start to cause issues in the future. and lastly remember on the partition properties to set up the backup details.
to create an ignorearchivebittrigger.txt file, easiest way to do it is add a line like this to your backup batch file
type nul > E:\Enterprise Vault Stores\YourVaultStore Ptn1\IgnoreArchiveBitTrigger.txt
but honestly, you may find that its just the type of backup you're running isn't clearing the Archive bits, so for instance in BE and NBU both do FULL backups, these remove the archive bit, and i *think* incremental also removes the archive bit, but a differential does not (i'm a bit fuzzy on which does and does not, so that might be reversed)
you may find that when you next do a full backup, that number will go down, or at least the contents of the watchfile table will be different
https://www.linkedin.com/in/alex-allen-turl-07370146