VSS snapshots are failing for specific volumes and the backups ultimately end as partially successful. You see the below error messages in the Replay Events and in Event Viewer with Event ID 4096.
Thread: 17212
Logger: tevoSource.snapshotHandler
Context: PG=VolsWithInterval720Minutes Volume=\\?\Volume{05e04add-aca3-11df-bdef-806e6f6e6963}\ DriveLetter=C:\Windows\SRPPartition
Source Location: SnapshotHandler.cpp:992
Details:
Transfer failed on volume: C:\Windows\SRPPartition Epoch: 5922 Target: SSI-FP-02 Port: 8001 - The device is not ready.
The error message in more detail:
Thread: 17212
Logger: tevoSource.snapshotHandler
Context: PG=VolsWithInterval720Minutes Volume=\\?\Volume{05e04add-aca3-11df-bdef-806e6f6e6963}\ DriveLetter=C:\Windows\SRPPartition
Source Location: SnapshotHandler.cpp:992
Details:
Transfer failed on volume: C:\Windows\SRPPartition Epoch: 5922 Target: SSI-FP-02 Port: 8001 - The device is not ready.
Thread: 17212
Logger: tevolib.tpalt
Context: PG=VolsWithInterval720Minutes Volume=\\?\Volume{05e04add-aca3-11df-bdef-806e6f6e6963}\ DriveLetter=C:\Windows\SRPPartition
Source Location: TransmitPacketsAlternative.cpp:470
Details:
ReadFile failed for the following elements:
Operation index: 9
Is Read: yes
TEVO_MESSAGE_HEADER:
nKbytesDone: 3520
nKBytesToDo: 34624
nOffset: 3748 blocks
nLength: 2097152 bytes
File Read:
File Offset: 30703616 bytes
Length: 2097152 bytes
OVERLAPPED members:
Offset: 30703616
OffsetHigh: 0
Offset (as 64-bit): 30703616