Your Windows Client Agent based Master backups fail. The failure may show up as a "Verify Failure" or "Incomplete Backup". If you review the Master backups files in the C:\PCBP directory (Master journal has the naming format of Mast_Month_Day_Hour_Minute_second.txt. Example: Mast_Nov_25-02_00_58.txt) you will find entries similar to the following:
C:\mount\Windows\System32\ServerManagerLauncher.exe, < 98.9% real data> C:\mount\Windows\System32\ServerTelemetryConfig.exe, < 100.0% real data> C:\mount\Windows\System32\ServerWerOptin.exe, <<scan failed>, <Not backed up>
These sparse files may also present their hardlinks to a path that no longer exists or is not accessible.
C:\mount\Windows\WinSxS\amd64_mchgr.inf_31bf3856ad364e35_6.3.9600.16384_none_05b90a2b2d434dac\ddsmc.sys is a hardlink to ===> | C:/mount/Windows/System32/DriverStore/FileRepository/mchgr.inf_amd64_6e053e26f7e6e8c3/ddsmc.sys
Research if this data is needed. If the data is needed, you will need to determine why it can not be called during a backup. There is a good chance the data is also not accessible to your Antivirus scans.
In the case of a migration from Windows Core to a full Windows 2012, the directory does not contain data that you will need for proper restoration of the Windows 2012 server. In this case excluding the C:\mount directory from your backup schedule, and running a new one time Master backup will correct the backup chain set.
These files are either not accessible by normal measure or are no longer existing on the system. The C:\mount directory could have been created as part of a software install or migration (example: to add a GUI to Core 2012).